Chapter renumber, and split ch 17

Renumber chapters 10a, 10b, 11, 12, 13, 14 -> 10, 11, 13, 12, [11,14].
Split ch 17 into a 17a and 17b; shuffle around im/mutable syntax to be consistent, and present it more slowly.
THe new immutable syntax is pushed through all later chapters

33 files changed, 1259 insertions, 1118 deletions

diff --git a/chapter21/README.md b/chapter21/README.md
index 18256cc6..5e7baaa1 100644
--- a/chapter21/README.md
+++ b/chapter21/README.md
@@ -99,7 +99,7 @@ relocation are two stages of the same obligation to make references correct.
 
 ## Execute the result
 
-Chapter 10b's lazy memory partitioning now carries through encoding. Parameters,
+Chapter 11's lazy memory partitioning now carries through encoding. Parameters,
 calls, and returns carry whole memory; `BulkMemPhi`, `MemPhi`, and `MemMerge`
 discover precise aliases inside each function. New consumes `{ctrl, $mem, size}`
 and produces `{ptr, $mem}`. Its memory covers the allocated struct's aliases;
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/Parser.java b/chapter21/src/main/java/com/seaofnodes/simple/Parser.java
index 3b502c44..d9071160 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/Parser.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/Parser.java
@@ -177,6 +177,10 @@ public class Parser {
      *  Parses a function body, assuming the header is parsed.
      */
     private ReturnNode parseFunctionBody(TypeFunPtr sig, Lexer loc, String... ids) {
+        return parseFunctionBody(sig, loc, null, ids);
+    }
+
+    private ReturnNode parseFunctionBody(TypeFunPtr sig, Lexer loc, java.util.BitSet finals, String... ids) {
         // Stack parser state on the local Java stack, and unstack it later
         Node oldctrl = ctrl().keep();
         Node oldmem  = _scope.mem().keep();
@@ -213,7 +217,7 @@ public class Parser {
         // All args, "as-if" called externally
         for( int i=0; i<ids.length; i++ ) {
             Type t = sig.arg(i);
-            _scope.define(ids[i], t, false, new ParmNode(ids[i],i+2,t,fun,con(t)).peephole(), loc);
+            _scope.define(ids[i], t, finals==null ? t instanceof TypeNil : finals.get(i), new ParmNode(ids[i],i+2,t,fun,con(t)).peephole(), loc);
         }
 
         // Parse the body
@@ -614,24 +618,23 @@ public class Parser {
         // outside the constructor need to check the final bit.
         if( _scope.in(def._idx)._type!=Type.TOP && def._final &&
             // Inside a constructor, final assign is OK, outside nope
-            !(_scope.inCon() && def._idx >= _scope._lexSize.last()) )
+            !_scope.canInit(def) )
             throw error("Cannot reassign final '"+name+"'");
 
         // Lift expression, based on type
-        Node lift = liftExpr(expr.keep(), def.type(), def._final);
+        Node lift = liftExpr(expr.keep(), def.type());
         // Update
         _scope.update(name,lift);
         // Return un-lifted expr
         return expr.unkeep();
     }
 
-    // Make finals deep; widen ints to floats; narrow wide int types.
+    // Apply declared access permissions; widen floats and narrow integers.
     // Early error if types do not match variable.
-    private Node liftExpr( Node expr, Type t, boolean xfinal ) {
+    private Node liftExpr( Node expr, Type t ) {
         assert !(expr._type instanceof TypeMemPtr tmp) || !tmp.isFRef();
-        // Final is deep on ptrs
-        if( xfinal && t instanceof TypeMemPtr tmp ) {
-            t = tmp.makeRO();
+        // Read-only access is deep; a fixed binding alone does not remove access.
+        if( t instanceof TypeMemPtr tmp && tmp.isFinal() ) {
             expr = peep(new ReadOnlyNode(expr));
         }
         // Auto-widen int to float
@@ -639,7 +642,7 @@ public class Parser {
         // Auto-narrow wide ints to narrow ints
         expr = zsMask(expr,t);
         // Type is sane
-        if( expr._type!=Type.BOTTOM && !expr._type.shallowISA(t) )
+        if( expr._type!=Type.BOTTOM && (!expr._type.shallowISA(t) || !expr._type.accessISA(t)) )
             throw error("Type " + expr._type.str() + " is not of declared type " + t.str());
         return expr;
     }
@@ -667,36 +670,44 @@ public class Parser {
         return require(n,";");
     }
 
-    /** Parse final: [!]var['=' asgn]
+    // Widen a reassignable binding without discarding the initializer's
+    // permissions. Lattice glb includes readonly memory and is too broad here.
+    private Type inferredType(Type t) {
+        if( t instanceof TypeMemPtr tmp ) {
+            Type base = TYPES.get(tmp._obj._name);
+            TypeMemPtr ptr = (TypeMemPtr)base;
+            return (tmp._ro ? ptr.makeRO() : ptr).makeNullable();
+        }
+        return t.glb();
+    }
+
+    // The binding modifier sits immediately before the name. It never
+    // changes permissions on the referenced object.
+    private boolean bindingFinal(Type t) {
+        if( match("!") ) return false;
+        if( match("~") ) return true;
+        return t==Type.TOP || t instanceof TypeNil;
+    }
+
+    /** Parse final: [!|~]var['=' asgn]
      */
     private Node parseDeclaration(Type t) {
         assert t!=null;
         // Has var/val instead of a user-declared type
         boolean inferType = t==Type.TOP || t==Type.BOTTOM;
-        boolean hasBang = match("!");
+        boolean xfinal = bindingFinal(t);
         Lexer loc = loc();
         String name = requireId();
         // Optional initializing expression follows
-        boolean xfinal = false;
         Node expr;
         if( match("=") ) {
             expr = parseAsgn();
-            // TOP means val and val is always final
-            xfinal = (t==Type.TOP) ||
-                // BOTTOM is var and var is always not-final
-                (t!=Type.BOTTOM &&
-                 // no Bang AND
-                 !hasBang &&
-                 // not-null (expecting null to be set to not-null)
-                 expr._type != Type.NIL &&
-                 // Pointers are final by default; int/flt are not-final by default.
-                 (t instanceof TypeNil));
             // var/val, then type comes from expression
             if( inferType ) {
                 if( expr._type==Type.NIL )
                     throw error("a not-null/non-zero expression");
                 t = expr._type;
-                if( !xfinal ) t = t.glb();  // Widen if not final
+                if( !xfinal ) t = inferredType(t);  // Widen if not final
             }
             if( t instanceof TypeFunPtr && expr._type instanceof TypeFunPtr tfp && tfp.isConstant() )
                 _code.link(tfp)._name = name;
@@ -712,8 +723,8 @@ public class Parser {
                 // Nullable pointers get a NIL; not-null get a TOP which
                 // signals that they *must* be initialized in the constructor.
             case TypeNil tn -> tn.nullable() ? NIL : con(Type.TOP);
-            case TypeInteger ti -> ZERO;
-            case TypeFloat tf -> con(TypeFloat.FZERO);
+            case TypeInteger ti -> xfinal ? con(Type.TOP) : ZERO;
+            case TypeFloat tf -> con(xfinal ? Type.TOP : TypeFloat.FZERO);
             // Bottom signals type inference: they must be initialized in
             // the constructor and that's when we'll discover the type.
             case Type tt -> { assert tt==Type.BOTTOM; yield con(tt); }
@@ -721,10 +732,7 @@ public class Parser {
         }
 
         // Lift expression, based on type
-        Node lift = liftExpr(expr, t, xfinal);
-
-        if( xfinal && t instanceof TypeMemPtr tmp )
-            t = tmp.makeRO();
+        Node lift = liftExpr(expr, t);
 
         // Lift type to the declaration.  This will report as an error later if
         // we cannot lift the type.
@@ -788,12 +796,14 @@ public class Parser {
     // t = int|i8|i16|i32|i64|u8|u16|u32|u64|byte|bool | flt|f32|f64 | val | var | struct[?]
     private Type type() {
         int old1 = pos();
+        boolean writable = match("!");
+        boolean readonly = !writable && match("~");
         // Only type with a leading `{` is a function pointer...
         if( peek('{') ) return typeFunPtr();
 
         // Otherwise you get a type name
         String tname = _lexer.matchId();
-        if( tname==null ) return null;
+        if( tname==null ) return posT(old1);
 
         // Convert the type name to a type.
         Type t0 = TYPES.get(tname);
@@ -802,6 +812,13 @@ public class Parser {
             return posT(old1);
         if( t0 == Type.BOTTOM || t0 == Type.TOP ) return t0; // var/val type inference
         Type t1 = t0 == null ? TypeMemPtr.make(TypeStruct.makeFRef(tname)) :t0; // Null: assume a forward ref type
+        // A qualifier before the name applies to the struct reference, not
+        // to an enclosing array. Arrays have their own [] / [~] qualifier.
+        if( t1 instanceof TypeMemPtr tmp ) {
+            if( readonly || !writable ) t1 = tmp.makeRO();
+        } else if( writable || readonly )
+            return posT(old1);
+
         // Nest arrays and '?' as needed
         Type t2 = t1;
         while( true ) {
@@ -810,6 +827,9 @@ public class Parser {
                     throw error("Type "+t0+" cannot be null");
                 if( tmp.nullable() ) throw error("Type "+t2+" already allows null");
                 t2 = tmp.makeNullable();
+            } else if( match("[~]") ) {
+                TypeMemPtr ary = typeAry(t2);
+                t2 = ary.makeFrom(ary._obj.makeRO()).makeRO();
             } else if( match("[]") ) {
                 t2 = typeAry(t2);
             } else
@@ -821,7 +841,7 @@ public class Parser {
         // Check valid forward ref, after parsing all the type extra bits.
         // Cannot check earlier, because cannot find required 'id' until after "[]?" syntax
         int old2 = pos();
-        match("!");
+        if( !match("!") ) match("~");
         String id = _lexer.matchId();
         if( !(peek(',') || peek(';') || match("->")) )
             return posT(old1);
@@ -829,7 +849,7 @@ public class Parser {
         if( id==null )
             return posT(old1);  // Reset lexer to reparse
         // Yes a forward ref, so declare it
-        TYPES.put(tname,t1);
+        TYPES.put(tname,((TypeMemPtr)t1).withAccess(false));
         return t2;
     }
 
@@ -839,7 +859,15 @@ public class Parser {
             throw error("Arrays of reference types must always be nullable");
         String tname = "["+t.str()+"]";
         Type ta = TYPES.get(tname);
-        if( ta != null ) return (TypeMemPtr)ta;
+        if( ta != null ) {
+            TypeStruct ary = ((TypeMemPtr)ta)._obj;
+            // Keep the original shallow struct reference.  Resolving a recursive
+            // struct must not expand its array element type on each lookup.
+            if( t instanceof TypeMemPtr ptr && (ptr._obj._fields==null || !ptr._obj.isAry()) &&
+                ary._fields[1]._type instanceof TypeMemPtr old )
+                t = old.withAccess(ptr._ro);
+            return TypeMemPtr.make(TypeStruct.makeAry(TypeInteger.U32,ary._fields[0]._alias,t,ary._fields[1]._alias));
+        }
         // Need make an array type.
         TypeStruct ts = TypeStruct.makeAry(TypeInteger.U32,_code.getALIAS(),t,_code.getALIAS());
         assert ts.str().equals(tname);
@@ -1109,7 +1137,7 @@ public class Parser {
         };
         // Convert to float ops, or narrow int types; error if not declared type.
         // Also, if postfix LHS is still keep()
-        return liftExpr(peep(op.widen()),t,false);
+        return liftExpr(peep(op.widen()),t);
     }
 
 
@@ -1239,6 +1267,8 @@ public class Parser {
     private void mem(Node n) { _scope.mem(n); }
 
     private void store(String name, int alias, Type glb, Node ptr, Node off, Node val, boolean init, Node ctrl) {
+        if( !init && ptr._type instanceof TypeMemPtr view && view._ro && ctrl()._type!=Type.XCONTROL )
+            throw error("Cannot modify final field '"+name+"'");
         Node prior = mem().keep();
         Node st = new StoreNode(loc(),name,alias,glb,prior,ptr,off,val,init);
         st.setDef(0,ctrl);
@@ -1278,7 +1308,7 @@ public class Parser {
         // Sanity check field name for existing
         TypeMemPtr tmp = (TypeMemPtr)TYPES.get(ptr._obj._name);
         if( tmp == null ) throw error("Accessing unknown field '" + name + "' from '" + ptr + "'");
-        TypeStruct base = tmp._obj;
+        TypeStruct base = ptr._obj.isAry() ? ptr._obj : tmp._obj;
         int fidx = base.find(name);
         if( fidx == -1 ) throw error("Accessing unknown field '" + name + "' from '" + ptr.str() + "'");
 
@@ -1299,7 +1329,7 @@ public class Parser {
         // Disambiguate "obj.fld==x" boolean test from "obj.fld=x" field assignment
         if( matchOpx('=','=') ) {
             Node val = parseAsgn().keep();
-            Node lift = liftExpr( val, tf, f._final );
+            Node lift = liftExpr( val, tf );
 
             store(name,f._alias,tf,expr.unkeep(),off.unkeep(),lift,false,base.isAry() ? ctrl() : null);
             return val.unkeep();        // "obj.a = expr" returns the expression while updating memory
@@ -1356,11 +1386,13 @@ public class Parser {
     private Node func() {
         Ary<Type> ts = new Ary<>(Type.class);
         Ary<String> ids = new Ary<>(String.class);
+        java.util.BitSet finals = new java.util.BitSet();
         _lexer.skipWhiteSpace();
         Lexer loc = loc();      // First argument location
         while( true ) {
             Type t = type();    // Arg type
             if( t==null ) break;
+            finals.set(ids.size(),bindingFinal(t));
             String id = requireId();
             ts .push(t );       // Push type/arg pairs
             ids.push(id);
@@ -1369,7 +1401,7 @@ public class Parser {
         require("->");
         // Make a concrete function type, with a fidx
         TypeFunPtr tfp = _code.makeFun(TypeTuple.make(ts.asAry()),Type.BOTTOM);
-        ReturnNode ret = parseFunctionBody(tfp,loc,ids.asAry());
+        ReturnNode ret = parseFunctionBody(tfp,loc,finals,ids.asAry());
         return con(ret._fun.sig());
     }
 
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/node/CallNode.java b/chapter21/src/main/java/com/seaofnodes/simple/node/CallNode.java
index 90999de3..70c71d43 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/node/CallNode.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/node/CallNode.java
@@ -161,7 +161,7 @@ public class CallNode extends CFGNode {
 
         // Check for args
         for( int i=0; i<tfp.nargs(); i++ )
-            if( !arg(i+2)._type.isa(tfp.arg(i)) )
+            if( !arg(i+2)._type.isa(tfp.arg(i)) || !arg(i+2)._type.accessISA(tfp.arg(i)) )
                 return Parser.error( "Argument #"+i+" isa "+arg(i+2)._type+", but must be a "+tfp.arg(i), _loc);
 
         return null;
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/node/LoadNode.java b/chapter21/src/main/java/com/seaofnodes/simple/node/LoadNode.java
index f668d2c3..f1a9cb07 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/node/LoadNode.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/node/LoadNode.java
@@ -54,8 +54,9 @@ public class LoadNode extends MemOpNode {
         Type t = MemMergeNode.contents(mem(),_alias,this);
         // Update declared forward ref to the actual.
         if( _declaredType.isFRef() && t instanceof TypeMemPtr tmp && !tmp.isFRef() )
-            _declaredType = tmp;
-        return err()==null ? _declaredType.join(t) : _declaredType;
+            _declaredType = tmp.withAccess(((TypeMemPtr)_declaredType)._ro);
+        Type rez = err()==null ? _declaredType.join(t) : _declaredType;
+        return ptr()._type.isFinal() || _declaredType.isFinal() ? rez.makeRO() : rez;
     }
 
     @Override
@@ -211,7 +212,7 @@ public class LoadNode extends MemOpNode {
 
     // Read-Only is a deep property, and cannot be cast-away
     private Node castRO(Node rez) {
-        if( ptr()._type.isFinal() && !rez._type.isFinal() )
+        if( (ptr()._type.isFinal() || _declaredType.isFinal()) && !rez._type.isFinal() )
             return new ReadOnlyNode(rez).peephole();
         return rez;
     }
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/node/ScopeNode.java b/chapter21/src/main/java/com/seaofnodes/simple/node/ScopeNode.java
index 2724d0a6..8d3e3089 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/node/ScopeNode.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/node/ScopeNode.java
@@ -125,6 +125,15 @@ public class ScopeNode extends Node {
     }
 
 
+    // Allocation fields live in the scope immediately outside the constructor
+    // block. Nested blocks retain that permission; surrounding bindings do not.
+    public boolean canInit(Var v) {
+        for( int i=_kinds._len-1; i>0; i-- )
+            if( _kinds.at(i)==Kind.Constructor )
+                return v._idx >= _lexSize.at(i-1) && v._idx < _lexSize.at(i);
+        return false;
+    }
+
     public boolean inCon() { return _kinds.last() == Kind.Constructor; }
 
     // Is v outside any current function scope?
@@ -209,7 +218,7 @@ public class ScopeNode extends Node {
                 : loop.setDef(v._idx,PhiNode.make(v._name, v.lazyGLB(), loop.ctrl(), loop.in(loop.update(v,null)._idx),null).peephole());
             setDef(v._idx,old);
         }
-        assert !v._final || st==null;
+        assert !v._final || st==null || canInit(v);
         if( st!=null ) setDef(v._idx,st); // Set new value
         return v;
     }
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/node/StoreNode.java b/chapter21/src/main/java/com/seaofnodes/simple/node/StoreNode.java
index f0cb3d1c..d56f1699 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/node/StoreNode.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/node/StoreNode.java
@@ -112,7 +112,7 @@ public class StoreNode extends MemOpNode {
         if( ptr()._type == Type.TOP )
             return null; // Dead store
         TypeMemPtr tmp = (TypeMemPtr)ptr()._type;
-        if( tmp._obj.field(_name)._final && !_init )
+        if( (tmp._ro || tmp._obj.field(_name)._final) && !_init )
             return Parser.error("Cannot modify final field '"+_name+"'",_loc);
         //Type t = val()._type;
         //return _init || t.isa(_declaredType) ? null : Parser.error("Cannot store "+t+" into field "+_declaredType+" "+_name,_loc);
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/type/Field.java b/chapter21/src/main/java/com/seaofnodes/simple/type/Field.java
index ffa9d2a6..c93f82e7 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/type/Field.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/type/Field.java
@@ -34,7 +34,7 @@ public class Field extends Type {
     public Field makeFrom( Type type ) {
         return type == _type ? this : new Field(_fname,type,_alias,_final).intern();
     }
-    @Override public Field makeRO() { return _final ? this : make(_fname,_type.makeRO(),_alias,true);  }
+    @Override public Field makeRO() { return isFinal() ? this : make(_fname,_type.makeRO(),_alias,true);  }
     @Override public boolean isFinal() { return _final && _type.isFinal(); }
 
     public static final Field TEST = make("test",Type.NIL,-2,false);
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/type/Type.java b/chapter21/src/main/java/com/seaofnodes/simple/type/Type.java
index 6df4e7ab..96b2c6ef 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/type/Type.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/type/Type.java
@@ -203,6 +203,10 @@ public class Type {
     /** Compute greatest lower bound in the lattice */
     public Type glb() { return Type.BOTTOM; }
 
+    // Writable array slots are invariant in their element access permissions.
+    // Otherwise an alias could insert a readonly pointer into a writable slot.
+    public boolean accessISA(Type dst) { return true; }
+
     // Is forward-reference
     public boolean isFRef() { return false; }
 
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/type/TypeMemPtr.java b/chapter21/src/main/java/com/seaofnodes/simple/type/TypeMemPtr.java
index bb2e2333..98e92bca 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/type/TypeMemPtr.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/type/TypeMemPtr.java
@@ -25,20 +25,41 @@ public class TypeMemPtr extends TypeNil {
     // (TOP   ,true ) - a nil
 
     public final TypeStruct _obj;
+    // Deep read-only access through this pointer; independent of slot finality.
+    public boolean _ro;
+
 
     private TypeMemPtr(byte nil, TypeStruct obj) {
         super(TMEMPTR,nil);
         assert obj!=null;
         _obj = obj;
+        _ro = obj==TypeStruct.BOT;
     }
     static TypeMemPtr make(byte nil, TypeStruct obj) { return new TypeMemPtr(nil, obj).intern(); }
     public static TypeMemPtr makeNullable(TypeStruct obj) { return make((byte)3, obj); }
     public static TypeMemPtr make(TypeStruct obj) { return new TypeMemPtr((byte)2, obj).intern(); }
-    public TypeMemPtr makeFrom(TypeStruct obj) { return obj==_obj ? this : make(_nil, obj); }
+    public TypeMemPtr makeFrom(TypeStruct obj) { return obj==_obj ? this : make(_nil, obj).withAccess(_ro); }
     public TypeMemPtr makeNullable() { return makeFrom((byte)3); }
-    @Override TypeMemPtr makeFrom(byte nil) { return nil==_nil ? this : make(nil,_obj); }
-    @Override public TypeMemPtr makeRO() { return makeFrom(_obj.makeRO()); }
-    @Override public boolean isFinal() { return _obj.isFinal(); }
+    @Override TypeMemPtr makeFrom(byte nil) { return nil==_nil ? this : make(nil,_obj).withAccess(_ro); }
+    @Override public TypeMemPtr makeRO() { return withAccess(true); }
+    @Override public boolean isFinal() { return _ro; }
+
+    public TypeMemPtr withAccess(boolean ro) {
+        if( _ro==ro ) return this;
+        TypeMemPtr ptr = new TypeMemPtr(_nil, _obj);
+        ptr._ro = ro;
+        return ptr.intern();
+    }
+
+    // Writable slots can load and store references, so their element access
+    // must agree in both directions. A read-only outer view can weaken access.
+    @Override public boolean accessISA(Type dst) {
+        if( !(dst instanceof TypeMemPtr ptr) ) return true;
+        if( _ro && !ptr._ro ) return false;
+        if( ptr._ro || _obj._fields==null || ptr._obj._fields==null || !_obj.isAry() || !ptr._obj.isAry() ) return true;
+        Type a = _obj._fields[1]._type, b = ptr._obj._fields[1]._type;
+        return a.accessISA(b) && b.accessISA(a);
+    }
 
     // An abstract pointer, pointing to either a Struct or an Array.
     // Can also be null or not, so 4 choices {TOP,BOT} x {nil,not}
@@ -47,43 +68,43 @@ public class TypeMemPtr extends TypeNil {
     public static final TypeMemPtr NOTBOT = make((byte)2,TypeStruct.BOT);
 
     public static final TypeMemPtr TEST= make((byte)2, TypeStruct.TEST);
-    public static void gather(ArrayList<Type> ts) { ts.add(NOTBOT); ts.add(BOT); ts.add(TEST); }
+    public static void gather(ArrayList<Type> ts) { ts.add(NOTBOT); ts.add(BOT); ts.add(TEST); ts.add(TEST.makeRO()); }
 
     @Override
     public TypeNil xmeet(Type t) {
         TypeMemPtr that = (TypeMemPtr) t;
-        return TypeMemPtr.make(xmeet0(that), (TypeStruct)_obj.meet(that._obj));
+        return TypeMemPtr.make(xmeet0(that), (TypeStruct)_obj.meet(that._obj)).withAccess(_ro | that._ro);
     }
 
     @Override
-    public TypeMemPtr dual() { return TypeMemPtr.make( dual0(), _obj.dual()); }
+    public TypeMemPtr dual() { return TypeMemPtr.make( dual0(), _obj.dual()).withAccess(!_ro); }
 
     // RHS is NIL; do not deep-dual when crossing the centerline
-    @Override Type meet0() { return _nil==3 ? this : make((byte)3,_obj); }
+    @Override Type meet0() { return _nil==3 ? this : make((byte)3,_obj).withAccess(_ro); }
 
 
     // True if this "isa" t up to named structures
     @Override public boolean shallowISA( Type t ) {
         if( !(t instanceof TypeMemPtr that) ) return false;
         if( this==that ) return true;
-        if( xmeet0(that)!=that._nil ) return false;
+        if( xmeet0(that)!=that._nil || (_ro && !that._ro) ) return false;
         if( _obj==that._obj ) return true;
         if( _obj._name.equals(that._obj._name) )
             return true;        // Shallow, do not follow matching names, just assume ok
         throw Utils.TODO(); // return _obj.shallowISA(that._obj);
     }
 
-    @Override public TypeMemPtr glb() { return make((byte)3,_obj.glb()); }
+    @Override public TypeMemPtr glb() { return make((byte)3,_obj.glb()).withAccess(true); }
     // Is forward-reference
     @Override public boolean isFRef() { return _obj.isFRef(); }
 
     @Override public int log_size() { return 3; } // (1<<3)==8-byte pointers
 
-    @Override int hash() { return _obj.hashCode() ^ super.hash(); }
+    @Override int hash() { return (_ro ? 8192 : 0) ^ _obj.hashCode() ^ super.hash(); }
 
     @Override boolean eq(Type t) {
         TypeMemPtr ptr = (TypeMemPtr)t; // Invariant
-        return _obj == ptr._obj  && super.eq(ptr);
+        return _ro==ptr._ro && _obj == ptr._obj  && super.eq(ptr);
     }
 
     @Override public String str() {
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/Chapter10Test.java b/chapter21/src/test/java/com/seaofnodes/simple/Chapter10Test.java
index 7da1354f..91505f41 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/Chapter10Test.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/Chapter10Test.java
@@ -25,7 +25,7 @@ public class Chapter10Test {
     // Issue #246: null-check guards start in Chapter 10; arrays arrive in Chapter 15.
     private static final String NULLABLE_POINT_SOURCE = """
         struct Point { int x; };
-        Point?[] !points = new Point?[2];
+        !Point?[] !points = new !Point?[2];
         points[arg] = new Point { x = 42; };
         Point? p = points[1];
         """;
@@ -101,7 +101,7 @@ struct Foo {
     int x;
 };
 Foo? foo = null;
-Bar !bar = new Bar;
+!Bar !bar = new Bar;
 bar.a = 1;
 bar.a = 2;
 return bar.a;
@@ -114,7 +114,7 @@ return bar.a;
     public void testExample() {
         CodeGen code = new CodeGen("""
 struct Vector2D { int x; int y; };
-Vector2D !v = new Vector2D;
+!Vector2D !v = new Vector2D;
 v.x = 1;
 if (arg)
     v.y = 2;
@@ -153,7 +153,7 @@ arg=0+new s0.0;
     public void testLoop() {
         CodeGen code = new CodeGen("""
 struct Bar { int a; };
-Bar !bar = new Bar;
+!Bar !bar = new Bar;
 while (arg) {
     bar.a = bar.a + 2;
     arg = arg + 1;
@@ -168,7 +168,7 @@ return bar.a;
     public void testIf() {
         CodeGen code = new CodeGen("""
 struct Bar { int a; };
-Bar !bar = new Bar;
+!Bar !bar = new Bar;
 if (arg) bar = null;
 bar.a = 1;
 return bar.a;
@@ -181,7 +181,7 @@ return bar.a;
     public void testIf2() {
         CodeGen code = new CodeGen("""
 struct Bar { int a; };
-Bar? !bar = null;
+!Bar? !bar = null;
 if (arg) bar = new Bar;
 bar.a = 1;
 return bar.a;
@@ -207,7 +207,7 @@ return bar.a;
     public void testIfOrNull() {
         CodeGen code = new CodeGen("""
 struct Bar { int a; };
-Bar? !bar = new Bar;
+!Bar? !bar = new Bar;
 if (arg) bar = null;
 if( bar ) bar.a = 1;
 return bar;
@@ -221,7 +221,7 @@ return bar;
         CodeGen code = new CodeGen(
 """
 struct Bar { int a; };
-Bar? !bar = new Bar;
+!Bar? !bar = new Bar;
 if (arg) bar = null;
 int rez = 3;
 if( !bar ) rez=4;
@@ -236,7 +236,7 @@ return rez;
     public void testWhileWithNullInside() {
         CodeGen code = new CodeGen("""
 struct s0 {int v0;};
-s0? !v0 = new s0;
+!s0? !v0 = new s0;
 int ret = 0;
 while(arg) {
     ret = v0.v0;
@@ -257,7 +257,7 @@ struct s0 {
     int v0;
 };
 s0? v1=new s0;
-s0? v1;
+!s0? !v1;
 v1=new s0;
 """);
         try { code.parse(); fail(); }
@@ -273,7 +273,7 @@ struct Iter {
     int x;
     int len;
 };
-Iter !i = new Iter;
+!Iter !i = new Iter;
 i.len = arg;
 int sum=0;
 while( i.x < i.len ) {
@@ -291,9 +291,9 @@ return sum;
     public void test1() {
         CodeGen code = new CodeGen("""
 struct s0 {int v0;};
-s0 !ret = new s0;
+!s0 !ret = new s0;
 while(arg) {
-    s0 !v0 = new s0;
+    !s0 !v0 = new s0;
     v0.v0 = arg;
     arg = arg-1;
     if (arg==5) ret=v0;
@@ -309,8 +309,8 @@ return ret;
     public void test2() {
         CodeGen code = new CodeGen("""
 struct s0 {int v0;};
-s0 !ret = new s0;
-s0 !v0 = new s0;
+!s0 !ret = new s0;
+!s0 !v0 = new s0;
 while(arg) {
     v0.v0 = arg;
     arg = arg-1;
@@ -328,9 +328,9 @@ return ret;
     public void test3() {
         CodeGen code = new CodeGen("""
 struct s0 {int v0;};
-s0 !ret = new s0;
+!s0 !ret = new s0;
 while(arg < 10) {
-    s0 !v0 = new s0;
+    !s0 !v0 = new s0;
     if (arg == 5) ret=v0;
     arg = arg + 1;
 }
@@ -455,9 +455,9 @@ return 0;
     @Test public void testReadBeforeStores() {
         var code = new CodeGen("""
             struct S { int x; int y; };
-            S !a = new S; S !b = new S;
+            !S !a = new S; !S !b = new S;
             a.x = 11; b.x = 22;
-            S !p = a; if (arg) p = b;
+            !S !p = a; if (arg) p = b;
             int before = p.x;
             a.y = 55; b.y = 66;
             a.x = 33; b.x = 44;
@@ -470,7 +470,7 @@ return 0;
 
     static final String NESTED_MEMORY = """
             struct S { int x; int y; int z; };
-            S !s = new S;
+            !S !s = new S;
             s.x = 5; s.y = 7; s.z = 11;
             while (arg > 0) {
                 s.x = s.x + 1;
@@ -499,7 +499,7 @@ return 0;
     @Test public void testMemoryAtEarlyReturns() {
         var code = new CodeGen("""
             struct S { int x; int y; int z; };
-            S !s = new S;
+            !S !s = new S;
             s.x = 3; s.y = 5; s.z = 7;
             if (arg) { s.x = 11; s.z = 13; return s; }
             s.y = 17;
@@ -514,9 +514,9 @@ return 0;
     @Test public void testKeepLoadsAtMerge() {
         var code = new CodeGen("""
             struct S { int x; };
-            S !a = new S; S !b = new S;
+            !S !a = new S; !S !b = new S;
             a.x = arg; b.x = arg+1;
-            S !p = a; S !q = b;
+            !S !p = a; !S !q = b;
             if (arg<0) { p=b; q=a; }
             int v;
             if (arg>1) v=p.x; else v=q.x;
@@ -533,7 +533,7 @@ return 0;
     @Test public void testDropStores() {
         var code = new CodeGen("""
             struct S { int x; };
-            S !s = new S;
+            !S !s = new S;
             if (arg) s.x=arg+1; else s.x=arg+2;
             return s;
             """).parse().opto();
@@ -546,9 +546,9 @@ return 0;
     @Test public void testKeepReadsBeforeWrites() {
         var code = new CodeGen("""
             struct S { int x; int y; };
-            S !a = new S; S !b = new S;
+            !S !a = new S; !S !b = new S;
             a.x=arg; b.x=arg+1;
-            S !p=a; S !q=b;
+            !S !p=a; !S !q=b;
             if (arg<0) { p=b; q=a; }
             int v;
             if (arg>1) { v=p.x; p.x=41; p.y=5; }
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/Chapter10bTest.java b/chapter21/src/test/java/com/seaofnodes/simple/Chapter10bTest.java
deleted file mode 100644
index 5d78ae06..00000000
--- a/chapter21/src/test/java/com/seaofnodes/simple/Chapter10bTest.java
+++ /dev/null
@@ -1,60 +0,0 @@
-package com.seaofnodes.simple;
-
-import com.seaofnodes.simple.codegen.*;
-import com.seaofnodes.simple.node.*;
-import org.junit.Test;
-import static org.junit.Assert.*;
-
-public class Chapter10bTest {
-    @Test public void testIndependentField() {
-        var code = new CodeGen("""
-            struct S { int x; int y; };
-            S !s = new S;
-            s.x = 42;
-            while (arg > 0) { s.y = s.y + arg; arg = arg - 1; }
-            return s.x;
-            """).parse().opto();
-        var stop = code._stop;
-        assertEquals("return 42;",stop.toString());
-        assertEquals("42",Eval2.eval(code,5));
-        assertNull(stop.walk(n -> n instanceof LoadNode ? n : null));
-    }
-
-    @Test public void testParallelMemoryPhis() {
-        var code = new CodeGen("""
-            struct S { int x; int y; int z; };
-            S !a = new S; S !b = new S;
-            S !p = a; if (arg) p = b;
-            while (arg > 0) {
-                a.x = p.x + arg;
-                a.y = p.y + 2;
-                a.z = p.z + 3;
-                arg = arg - 1;
-            }
-            return a;
-            """).parse().opto();
-        var stop = code._stop;
-        int[] phis = {0};
-        stop.walk(n -> {
-            if (n instanceof MemPhiNode) phis[0]++;
-            if (n instanceof MemMergeNode m && m.in(1) instanceof BulkMemPhiNode b)
-                for(int a=b._aliases.nextSetBit(0); a>=0; a=b._aliases.nextSetBit(a+1))
-                    assertTrue(a<m.nIns() && m.in(a)!=null);
-            assertFalse(n instanceof PhiNode && n.isMem() &&
-                !(n instanceof MemPhiNode) && !(n instanceof BulkMemPhiNode) && !(n instanceof ParmNode));
-            return null;
-        });
-        assertTrue(phis[0]>=3);
-        assertEquals("S{x=1,y=2,z=3}",Eval2.eval(code,4));
-    }
-
-    @Test public void testLateSliceWorklist() {
-        // Seed 97 exposed a store selecting a bulk predecessor without queuing
-        // it. Keep both the worklist assertion and the final heap check.
-        for (int seed : new int[]{0,97,123,456}) {
-            var code = new CodeGen(Chapter10Test.NESTED_MEMORY,com.seaofnodes.simple.type.TypeInteger.BOT,seed).parse();
-            code.opto();
-            assertEquals("S{x=9,y=25,z=17}",Eval2.eval(code,4));
-        }
-    }
-}
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/Chapter11Test.java b/chapter21/src/test/java/com/seaofnodes/simple/Chapter11Test.java
index 6142624b..a38e93c1 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/Chapter11Test.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/Chapter11Test.java
@@ -1,553 +1,60 @@
 package com.seaofnodes.simple;
-import com.seaofnodes.simple.codegen.CodeGen;
-import com.seaofnodes.simple.print.IRPrinter;
-
 
+import com.seaofnodes.simple.codegen.*;
+import com.seaofnodes.simple.node.*;
 import org.junit.Test;
-import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.*;
 
 public class Chapter11Test {
-
-    // A placeholder test used to rapidly rotate through fuzzer produced issues
-    @Test
-    public void testFuzzer() {
-        CodeGen code = new CodeGen(
-"""
-while(---- -arg) {
-    while(-arg) {
-        while(-----arg*---0) {
-                int N=--false==false<--arg;
-                while(N<-4==N) {
-                    N=N+N;
-                }
-            }
-        {
-            int kzEl_r7EYz=3*----0!=-arg<(37*--97!=0/arg==arg)<=-(--arg!=0);
-            while(kzEl_r7EYz<---1) {
-                kzEl_r7EYz=kzEl_r7EYz+kzEl_r7EYz*arg>=24;
-                if(7) continue;
-                kzEl_r7EYz=false;
-                if(-kzEl_r7EYz+arg<-3) continue;
-                else {
-                    while(kzEl_r7EYz) continue;
-                    arg=----3;
-                    kzEl_r7EYz=-(-----arg*1>-kzEl_r7EYz);
-                    int v2uF_4ba=9;
-                }
-            }
-        }
-        int pjcp7rv=arg;
-        {
-            int m2ya3=--arg-pjcp7rv;
-            while(m2ya3<-----pjcp7rv>=pjcp7rv+--pjcp7rv!=---pjcp7rv!=-arg<---(-m2ya3)>m2ya3<=-----true>14!=--m2ya3) {
-                m2ya3=m2ya3+-(--0<=false<pjcp7rv/arg<=-true);
-                while((--m2ya3)<--arg<-----arg*false!=arg<pjcp7rv*arg) {
-                    pjcp7rv=-3+-arg;
-                    break;
-                }
-                while(-3) {
-                    while(67+0-61) m2ya3=m2ya3;
-                    if(----pjcp7rv==---(---arg)) pjcp7rv=0!=-23;
-                    else pjcp7rv=----89;
-                    while(m2ya3!=m2ya3<pjcp7rv) m2ya3=1;
-                    while(--arg<=pjcp7rv) pjcp7rv=-32<=-m2ya3+62;
-                }
-                break;
-            }
-        }
-        {
-            int arg=-1<-9!=(-arg>=-pjcp7rv>=arg<=arg);
-            while(arg<-arg) {
-                arg=arg+--arg;
-                {
-                    while((--93)--pjcp7rv*-pjcp7rv+arg) arg=0-(6>=(--(---41/(0))!=--pjcp7rv)>=---2*33);
-                    pjcp7rv=11;
-                    int c=pjcp7rv;
-                    if(--107) break;
-                    else break;
-                }
-            }
-        }
-        pjcp7rv=pjcp7rv;
-        int aR0Wkua=-pjcp7rv==pjcp7rv;
-        {
-            if(-0!=-0) while(-true) break;
-            else {
-                while(aR0Wkua) pjcp7rv=-0/pjcp7rv;
-                pjcp7rv=pjcp7rv;
-            }
-        }
-    }
-    if(-arg) {
-        {
-            int Isdlt0fr91=0!=arg;
-            while(Isdlt0fr91<-Isdlt0fr91==-Isdlt0fr91+true) {
-                Isdlt0fr91=Isdlt0fr91+-1!=true;
-                if(-arg) if(--arg<=Isdlt0fr91) Isdlt0fr91=-Isdlt0fr91;
-                int i=---arg<---arg!=--40;
-                {
-                    int jVX43Ln4Dm=-(6)==-Isdlt0fr91/----0;
-                    while(jVX43Ln4Dm<--(3-3)) {
-                        jVX43Ln4Dm=jVX43Ln4Dm+-0<25;
-                        i=24<--(jVX43Ln4Dm);
-                    }
-                }
-                i=(arg!=----false>=7);
-                int Te=5>-arg;
-                break;
-            }
-        }
-        arg=arg!=--true/arg;
-        {
-            int UX=arg;
-            while(UX<-3*arg) {
-                UX=UX+arg/-1;
-                arg=-3--(-UX- -47<arg==--arg==arg)/arg- -UX>=-arg;
-                if(---12) while(-UX) break;
-                break;
-            }
-        }
-        continue;
-    }
-    if(arg) arg=--0;
-    else if(1) continue;
-    int DtTlhjYq=19==arg;
-    {
-        arg=--DtTlhjYq<=(DtTlhjYq/---DtTlhjYq<=-DtTlhjYq);
-        if(---arg) continue;
-        else {
-                int Zsl=40;
-                while(Zsl<--Zsl--false>((Zsl))==Zsl!=--DtTlhjYq-DtTlhjYq-DtTlhjYq) {
-                    Zsl=Zsl+arg;
-                }
-            }
-        if((arg)) if(-DtTlhjYq) {
-            }
-            else while(((2)==3*arg/DtTlhjYq)<=0==---arg) return false;
-        else {
-                int lwbF=arg>=0;
-                while(lwbF<57) {
-                    lwbF=lwbF+--(-arg+lwbF)>=-2>=arg!=arg;
-                    arg=----0+0;
-                    while(49) break;
-                    if(true) DtTlhjYq=-----arg;
-                    DtTlhjYq=0!=-----(0);
-                }
-            }
-        arg=---arg!=DtTlhjYq/--0;
-        DtTlhjYq=-DtTlhjYq/(--arg<arg);
-        if(32) {
-                int q=-DtTlhjYq;
-                while(q<arg*(0*q)/0) {
-                    q=q+DtTlhjYq;
-                    DtTlhjYq=arg;
-                }
-            }
-        else if(--arg) if(15) break;
-                else arg=0==arg<=-55>DtTlhjYq;
-            else {
-            }
-        DtTlhjYq=-0;
-        {
-            while((0)<-arg) DtTlhjYq=-DtTlhjYq;
-        }
-        if(30/--(arg)>=0) DtTlhjYq=-0>=arg;
-        else {
-            int Y2wcIQJ=--DtTlhjYq*---11;
-            if(arg==arg) {
-                Y2wcIQJ=-----Y2wcIQJ;
-                Y2wcIQJ=Y2wcIQJ<7;
-                if(DtTlhjYq) arg=arg;
-                else break;
-                while(-arg!=-31==(false<=-15>=-DtTlhjYq+--6*-----Y2wcIQJ<=---arg!=-Y2wcIQJ<=---0<-arg*--Y2wcIQJ)) DtTlhjYq=arg!=3;
-            }
-            continue;
-        }
-        arg=DtTlhjYq;
-        arg=--3/(---arg)>=80>=-DtTlhjYq<=DtTlhjYq;
-        arg=51+---(-true)!=arg!=----1==-DtTlhjYq;
-        if(11<=arg) if((arg)+79<32+(-arg)) continue;
-            else if(true==DtTlhjYq) break;
-        break;
-    }
-}
-if(arg!=62==arg) {
-    while(---arg) {
-        {
-            int bhmDacPM=arg/arg;
-            while(bhmDacPM<arg) {
-                bhmDacPM=bhmDacPM+80*((-bhmDacPM)/---bhmDacPM>1)<bhmDacPM-2!=7;
-                arg=-0;
-                arg=bhmDacPM>=-arg+-arg;
-                break;
-            }
-        }
-        int arg=true;
-        arg=arg<=arg;
-        {
-            int KlC=30;
-            while(KlC<-2) {
-                KlC=KlC+-1!=25<=-KlC>KlC>----0;
-                int Ij=arg>=-arg<=---10;
-                {
-                    int LAbgurVa2R=-arg!=Ij;
-                    while(LAbgurVa2R<-true) {
-                        LAbgurVa2R=LAbgurVa2R+Ij;
-                        KlC=-LAbgurVa2R;
-                        Ij=42*(-Ij>true);
-                        while(Ij) arg=KlC;
-                        KlC=-----7>-(--KlC<--7)==-LAbgurVa2R;
-                    }
-                }
-                int a=Ij<=-KlC;
-                if(Ij) {
-                    int r1W=a!=-false;
-                }
-                else {
-                    arg=56>=Ij;
-                    while(54) break;
-                    arg=8>=-(a<--Ij)/a>=-a-KlC;
-                }
-                int Yt_T=KlC;
-                arg=KlC;
-            }
-        }
-        if(----false/--arg/12+-----0) if(-9+-arg) while(arg!=(arg)) arg=--1>=-71-arg!=---(--arg*11+102)/--arg;
-            else if(----arg) continue;
-        if(-arg-arg) {
-            arg=-(-arg)*--(-3)<(-7==-arg----arg);
-            {
-                int arg=arg;
-                while(arg<-0>arg==-arg-(-arg>1+11)) {
-                    arg=arg+6-arg!=--0>---30>=---arg<=arg/(3)+---arg;
-                }
-            }
-            arg=-arg+arg;
-            arg=--47+-arg<1>arg*(-arg==-arg- -0>3);
-            arg=(----arg)!=arg+--59;
-            arg=- -4+arg==-(arg)-arg;
-        }
-        else {
-            while(--true-----true*-25+-18>arg>=-----(-arg)---13) {
-                arg=-0+--true<false;
-                continue;
-            }
-            arg=true<=arg;
-            break;
-        }
-        arg=arg*22<--(0+-arg);
-        {
-            continue;
+    @Test public void testIndependentField() {
+        var code = new CodeGen("""
+            struct S { int x; int y; };
+            !S !s = new S;
+            s.x = 42;
+            while (arg > 0) { s.y = s.y + arg; arg = arg - 1; }
+            return s.x;
+            """).parse().opto();
+        var stop = code._stop;
+        assertEquals("return 42;",stop.toString());
+        assertEquals("42",Eval2.eval(code,5));
+        assertNull(stop.walk(n -> n instanceof LoadNode ? n : null));
+    }
+
+    @Test public void testParallelMemoryPhis() {
+        var code = new CodeGen("""
+            struct S { int x; int y; int z; };
+            !S !a = new S; !S !b = new S;
+            !S !p = a; if (arg) p = b;
+            while (arg > 0) {
+                a.x = p.x + arg;
+                a.y = p.y + 2;
+                a.z = p.z + 3;
+                arg = arg - 1;
+            }
+            return a;
+            """).parse().opto();
+        var stop = code._stop;
+        int[] phis = {0};
+        stop.walk(n -> {
+            if (n instanceof MemPhiNode) phis[0]++;
+            if (n instanceof MemMergeNode m && m.in(1) instanceof BulkMemPhiNode b)
+                for(int a=b._aliases.nextSetBit(0); a>=0; a=b._aliases.nextSetBit(a+1))
+                    assertTrue(a<m.nIns() && m.in(a)!=null);
+            assertFalse(n instanceof PhiNode && n.isMem() &&
+                !(n instanceof MemPhiNode) && !(n instanceof BulkMemPhiNode) && !(n instanceof ParmNode));
+            return null;
+        });
+        assertTrue(phis[0]>=3);
+        assertEquals("S{x=1,y=2,z=3}",Eval2.eval(code,4));
+    }
+
+    @Test public void testLateSliceWorklist() {
+        // Seed 97 exposed a store selecting a bulk predecessor without queuing
+        // it. Keep both the worklist assertion and the final heap check.
+        for (int seed : new int[]{0,97,123,456}) {
+            var code = new CodeGen(Chapter10Test.NESTED_MEMORY,com.seaofnodes.simple.type.TypeInteger.BOT,seed).parse();
+            code.opto();
+            assertEquals("S{x=9,y=25,z=17}",Eval2.eval(code,4));
         }
     }
-    arg=1*---((3<=true)==---2);
-    arg=7+-(-1);
-    return arg+--true;
-}
-else {
-    int o3ypEsewxM=-(---arg);
-    int vzXB=(-(---11<=--o3ypEsewxM>=--0))<=-0/-arg;
-    int L=-arg;
-    int B4mHcrf=---vzXB;
-    int oZWGdzZl=-o3ypEsewxM;
-    int K6tQqa1=11;
-    while(0!=--L) {
-            int sdZfTM=vzXB*true+K6tQqa1;
-            while(sdZfTM<false) {
-                sdZfTM=sdZfTM+arg;
-                sdZfTM=oZWGdzZl;
-                K6tQqa1=-K6tQqa1;
-                arg=---K6tQqa1;
-                while((3+-K6tQqa1)<oZWGdzZl) {
-                    if(-----(-1)) sdZfTM=-false;
-                    {}
-                }
-                K6tQqa1=vzXB!=-(B4mHcrf+-7>false);
-                sdZfTM=vzXB;
-            }
-        }
-    L=false;
-    while(31) B4mHcrf=arg;
-    oZWGdzZl=-0<--oZWGdzZl<=--2;
-    if(K6tQqa1>=20<=46) {
-        if(-1+-L) if(oZWGdzZl) {
-                int wmhv=-----0;
-            }
-        int arg=0;
-        o3ypEsewxM=---(oZWGdzZl);
-        return -oZWGdzZl/0;
-    }
-    else if(arg) {
-            int yKk5=B4mHcrf>=4>K6tQqa1<-B4mHcrf/o3ypEsewxM;
-            return -K6tQqa1;
-        }
-        else {
-            if(---0) {
-                {}
-                {}
-            }
-            return o3ypEsewxM;
-        }
-}
-""");
-        code.parse().opto().typeCheck().GCM();
-        assertEquals("return 9;", code.print());
-    }
-
-
-    @Test
-    public void testPrimes() {
-        CodeGen code = new CodeGen(
-"""
-if( arg < 2 ) return 0;
-int primeCount = 1;
-int prime = 3;
-while( prime <= arg ) {
-    int isPrime = 1;
-    // Check for even case, so the next loop need only check odds
-    if( (prime/2)*2 == prime )
-        continue;
-    // Check odds up to sqrt of prime
-    int j = 3;
-    while( j*j <= prime ) {
-        if( (prime/j)*j == prime ) {
-            isPrime = 0;
-            break;
-        }
-        j = j + 2;
-    }
-    if( isPrime )
-        primeCount = primeCount + 1;
-    prime = prime + 2;
-}
-return primeCount;
-""");
-        code.parse().opto();
-        assertEquals("return Phi(Region,0,Phi(Loop,1,Phi(Region,Phi_primeCount,Phi_primeCount,(Phi_primeCount+1))));", code.print());
-        assertEquals("0", Eval2.eval(code,  1)); // No primes 1 or below
-        assertEquals("1", Eval2.eval(code,  2)); // 2
-        assertEquals("2", Eval2.eval(code,  3)); // 2, 3
-        assertEquals("2", Eval2.eval(code,  4)); // 2, 3
-        assertEquals("3", Eval2.eval(code,  5)); // 2, 3, 5
-        assertEquals("4", Eval2.eval(code, 10)); // 2, 3, 5, 7
-    }
-
-    @Test
-    public void testAntiDeps1() {
-        CodeGen code = new CodeGen(
-"""
-struct S { int f; };
-S !v=new S;
-v.f = 2;
-int i=new S.f;
-i=v.f;
-if (arg) v.f=1;
-return i;
-""");
-        code.parse().opto();
-        assertEquals("return 2;", code.print());
-        assertEquals("2", Eval2.eval(code, 0));
-        assertEquals("2", Eval2.eval(code, 1));
-    }
-
-    @Test
-    public void testAntiDeps2() {
-        CodeGen code = new CodeGen(
-"""
-struct S { int f; };
-S !v = new S;
-v.f = arg;
-S !t = new S;
-int i = 0;
-if (arg) {
-    if (arg+1) v = t;
-    i = v.f;
-} else {
-    v.f = 2;
-}
-return i;
-""");
-        code.parse().opto();
-        assertEquals("return Phi(Region,.f,0);", code.print());
-    }
-
-    @Test
-    public void testAntiDeps3() {
-        CodeGen code = new CodeGen(
-"""
-struct S { int f; };
-S !v0 = new S;
-S? v1;
-if (arg) v1 = new S;
-if (v1) {
-    v0.f = v1.f;
-} else {
-    v0.f = 2;
-}
-return v0;
-""");
-        code.parse().opto();
-        assertEquals("return S;", code.print());
-    }
-
-
-    @Test
-    public void testAntiDeps4() {
-        CodeGen code = new CodeGen(
-"""
-struct S { int f; };
-S !v = new S;
-v.f = arg;
-S t = new S;
-int i = v.f;
-if (arg+1) arg= 0;
-while (arg) v.f = 2;
-return i;
-""");
-        code.parse().opto();
-        assertEquals("return arg;", code.print());
-    }
-
-    @Test
-    public void testAntiDeps5() {
-        CodeGen code = new CodeGen(
-"""
-struct S { int f; };
-S !v = new S;
-while(1) {
-    while(arg+1) { arg=arg-1; }
-    if (arg) break;
-    v.f = 2;
-}
-return v;
-""");
-        code.parse().opto();
-        assertEquals("return S;", code.print());
-    }
-
-    @Test
-    public void testAntiDeps6() {
-        CodeGen code = new CodeGen(
-"""
-struct s { int v; };
-s !ptr=new s;
-while( -arg )
-  ptr = new s;
-while(1)
-  arg = arg+ptr.v;
-""");
-        code.parse().opto();
-        assertEquals("return Top;", code.print());
-    }
-
-    @Test
-    public void testAntiDeps7() {
-        CodeGen code = new CodeGen(
-"""
-struct S { int f; };
-S !v = new S;
-S t = new S;
-int i = v.f;
-while (arg) {
-    v.f = arg;
-    arg = arg-1;
-}
-return i;
-""");
-        code.parse().opto();
-        assertEquals("return 0;", code.print());
-    }
-
-    @Test
-    public void testAntiDeps8() {
-        CodeGen code = new CodeGen(
-"""
-struct S { int f; };
-S !v = new S;
-S t = new S;
-while(arg) {
-    arg=arg-1;
-    int f = v.f;
-    v.f = 2;
-    if (arg) arg = f;
-    else v.f = 3;
-}
-return arg;
-""");
-        code.parse().opto();
-        assertEquals("return 0;", code.print());
-    }
-
-    @Test
-    public void testAntiDeps9() {
-        CodeGen code = new CodeGen(
-"""
-struct S { int f; };
-S !v = new S;
-S t = new S;
-if (arg) {
-    v.f=2;
-    int i=t.f;
-    v.f=i;
-}
-return v;
-""");
-        code.parse().opto();
-        assertEquals("return S;", code.print());
-    }
-
-    @Test
-    public void testExample2() {
-        CodeGen code = new CodeGen(
-"""
-struct S { int f; };
-S !v = new S;
-int i = arg;
-while (arg > 0) {
-    int j = i/3;
-    if (arg == 5)
-        v.f = j;
-    arg = arg - 1;
-}
-return v;
-                """);
-        code.parse().opto();
-        //assertEquals("return new S;", code.print());
-    }
-
-    @Test
-    public void testScheduleUse() {
-        CodeGen code = new CodeGen(
-"""
-int v0=0;
-while(0>=0) {
-    u1 v1=0;
-    v1=v0;
-    if(v1*0)
-        v0=-v1;
-}
-return 0;
-""");
-        code.parse().opto();
-        assertEquals("return Top;", code.print());
-    }
-
-    @Test
-    public void testLoopCarriedDep() {
-        CodeGen code = new CodeGen(
-"""
-u32 v0=0;
-{
-    int v1=0;
-    while(v1) {
-        v1=1>>>v0!=0;
-        v0=v1/0;
-    }
-    return v1;
-}
-""");
-        code.parse().opto();
-        assertEquals("return 0;", code.print());
-    }
-
 }
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/Chapter12Test.java b/chapter21/src/test/java/com/seaofnodes/simple/Chapter12Test.java
index c50be559..f2078d03 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/Chapter12Test.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/Chapter12Test.java
@@ -1,82 +1,261 @@
 package com.seaofnodes.simple;
 
 import com.seaofnodes.simple.codegen.CodeGen;
-import com.seaofnodes.simple.node.StopNode;
 import org.junit.Test;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.fail;
 
 public class Chapter12Test {
-    @Test public void testSubZeroFloat() {
-        var code = new CodeGen("flt x = arg; return 0-x;").parse().opto().typeCheck();
-        // Compare strings so +0.0 and -0.0 remain distinct.
-        assertEquals("0.0", Eval2.eval(code,0));
-        assertEquals("-1.0", Eval2.eval(code,1));
+    @Test
+    public void testJig() {
+        CodeGen code = new CodeGen(
+"""
+return 3.14;
+""");
+        code.parse().opto();
+        assertEquals("return 3.14;", code.print());
+        assertEquals("3.14", Eval2.eval(code,  0));
     }
 
-    @Test public void testDeadNumericReturns() {
-        for( String[] test : new String[][] {
-            {"if(1) return 7; else return 2.5;", "7"},
-            {"if(0) return 7; else return 2.5;", "2.5"},
-            {"return 7; return 2.5;", "7"},
-            {"return 2.5; return 7;", "2.5"}
-        } ) {
-            String src = test[0];
-            var code = new CodeGen(src).parse().opto().typeCheck();
-            assertEquals(src,test[1],Eval2.eval(code,0));
-        }
+    @Test
+    public void testLinkedList0() {
+        CodeGen code = new CodeGen(
+"""
+struct LLI { !LLI? !next; int i; };
+!LLI? !head = null;
+while( arg ) {
+    !LLI !x = new LLI;
+    x.next = head;
+    x.i = arg;
+    head = x;
+    arg = arg-1;
+}
+return head.next.i;
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Might be null accessing 'next'",e.getMessage()); }
     }
 
+    @Test
+    public void testLinkedList1() {
+        CodeGen code = new CodeGen(
+"""
+struct LLI { !LLI? !next; int i; };
+!LLI? !head = null;
+while( arg ) {
+    !LLI !x = new LLI;
+    x.next = head;
+    x.i = arg;
+    head = x;
+    arg = arg-1;
+}
+if( !head ) return 0;
+LLI? next = head.next;
+if( next==null ) return 1;
+return next.i;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,0,1,.i);", code.print());
+        assertEquals("2", Eval2.eval(code,  3));
+    }
 
     @Test
-    public void testJig() {
+    public void testCoRecur() {
         CodeGen code = new CodeGen(
 """
-return 3.14;
+struct int0 { int i; !flt0? !f; };
+struct flt0 { flt f; !int0? !i; };
+!int0 !i0 = new int0;
+i0.i = 17;
+!flt0 !f0 = new flt0;
+f0.f = 3.14;
+i0.f = f0;
+f0.i = i0;
+return f0.i.f.i.i;
 """);
         code.parse().opto();
-        assertEquals("return 3.14;", code.print());
-        assertEquals("3.14", Eval2.eval(code,  0));
+        assertEquals("return 17;", code.print());
     }
 
     @Test
-    public void testFloat() {
+    public void testNullRef0() {
         CodeGen code = new CodeGen(
 """
-return 3.14;
+struct N { !N? !next; int i; };
+N n = new N;
+return n.next;
 """);
         code.parse().opto();
-        assertEquals("return 3.14;", code.print());
-        assertEquals("3.14", Eval2.eval(code,  0));
+        assertEquals("return null;", code.print());
     }
 
     @Test
-    public void testSquareRoot() {
+    public void testNullRef1() {
         CodeGen code = new CodeGen(
 """
-flt guess = arg;
-while( 1 ) {
-    flt next = (arg/guess + guess)/2;
-    if( next == guess ) break;
-    guess = next;
-}
-return guess;
+struct M { int m; };
+struct N { !M !next; int i; };
+N n = new N { next = new M; };
+return n.next;
 """);
         code.parse().opto();
-        assertEquals("return Phi(Loop,(flt)arg,(((ToFloat/Phi_guess)+Phi_guess)*0.5f));", code.print());
-        assertEquals("3.0", Eval2.eval(code,  9));
-        assertEquals("1.414213562373095", Eval2.eval(code,  2));
+        assertEquals("return (const)M;", code.print());
     }
 
     @Test
-    public void testFPOps() {
+    public void testNullRef2() {
         CodeGen code = new CodeGen(
 """
-flt x = arg;
-return x+1==x;
+struct M { int m; };
+struct N { !M !next; int i; };
+N n = new N { next = null; }
+return n.next;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Type null is not of declared type *M",e.getMessage()); }
+    }
+
+    @Test
+    public void testNullRef3() {
+        CodeGen code = new CodeGen(
+"""
+struct N { !N? !next; int i; };
+!N !n = new N;
+n.i = 3.14;
+return n.i;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Type 3.14 is not of declared type int",e.getMessage()); }
+    }
+
+    @Test
+    public void testNullRef4() {
+        CodeGen code = new CodeGen("-null-5/null-5;");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot 'Add' null",e.getMessage()); }
+    }
+
+    @Test public void testNullRef5() {
+        CodeGen code = new CodeGen("return null+42;");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot 'Add' null",e.getMessage()); }
+    }
+
+    @Test
+    public void testEmpty() {
+        CodeGen code = new CodeGen(
+"""
+struct S{};
 """);
         code.parse().opto();
-        assertEquals("return ((flt)arg==(ToFloat+1.0f));", code.print());
-        assertEquals("0", Eval2.eval(code, 1));
+        assertEquals("return 0;", code.print());
+        assertEquals("0", Eval2.eval(code,  0));
     }
+
+    @Test
+    public void testForwardRef0() {
+        CodeGen code = new CodeGen(
+"""
+struct S1 { !S2? !s; };
+return new S2;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Unknown struct type 'S2'",e.getMessage()); }
+    }
+
+    @Test
+    public void testForwardRef1() {
+        CodeGen code = new CodeGen(
+"""
+struct S1 { !S2? !s; };
+struct S2 { int x; };
+return new S1.s=new S2;
+""");
+        code.parse().opto();
+        assertEquals("return S2;", code.print());
+    }
+
+    @Test
+    public void testcheckNull() {
+        CodeGen code = new CodeGen(
+"""
+struct I {int i;};
+struct P { !I? !pi; };
+!P !p1 = new P;
+!P !p2 = new P;
+p2.pi = new I;
+p2.pi.i = 2;
+if (arg) p1 = new P;
+return p1.pi.i + 1;
+""");
+        try { code.parse().opto().typeCheck();  fail(); }
+        catch( Exception e ) {  assertEquals("Might be null accessing 'i'",e.getMessage());  }
+    }
+
+    @Test
+    public void testCoRecur2() {
+        CodeGen code = new CodeGen(
+"""
+struct A { !L? !a; !T? !b; !F? !c; };  !A? !a = new A;
+struct B { !M? !a; !U? !b; !G? !c; };  !B? !b = new B;
+struct C { !N? !a; !V? !b; !H? !c; };  !C? !c = new C;
+struct D { !O? !a; !W? !b; !I? !c; };  !D? !d = new D;
+struct E { !P? !a; !X? !b; !J? !c; };  !E? !e = new E;
+struct F { !Q? !a; !Y? !b; !K? !c; };  !F? !f = new F;
+struct G { !R? !a; !Z? !b; !L? !c; };  !G? !g = new G;
+struct H { !S? !a; !A? !b; !M? !c; };  !H? !h = new H;
+struct I { !T? !a; !B? !b; !N? !c; };  !I? !i = new I;
+struct J { !U? !a; !C? !b; !O? !c; };  !J? !j = new J;
+struct K { !V? !a; !D? !b; !P? !c; };  !K? !k = new K;
+struct L { !W? !a; !E? !b; !Q? !c; };  !L? !l = new L;
+struct M { !X? !a; !F? !b; !R? !c; };  !M? !m = new M;
+struct N { !Y? !a; !G? !b; !S? !c; };  !N? !n = new N;
+struct O { !Z? !a; !H? !b; !T? !c; };  !O? !o = new O;
+struct P { !A? !a; !I? !b; !U? !c; };  !P? !p = new P;
+struct Q { !B? !a; !J? !b; !V? !c; };  !Q? !q = new Q;
+struct R { !C? !a; !K? !b; !W? !c; };  !R? !r = new R;
+struct S { !D? !a; !L? !b; !X? !c; };  !S? !s = new S;
+struct T { !E? !a; !M? !b; !Y? !c; };  !T? !t = new T;
+struct U { !F? !a; !N? !b; !Z? !c; };  !U? !u = new U;
+struct V { !G? !a; !O? !b; !A? !c; };  !V? !v = new V;
+struct W { !H? !a; !P? !b; !B? !c; };  !W? !w = new W;
+struct X { !I? !a; !Q? !b; !C? !c; };  !X? !x = new X;
+struct Y { !J? !a; !R? !b; !D? !c; };  !Y? !y = new Y;
+struct Z { !K? !a; !S? !b; !E? !c; };  !Z? !z = new Z;
+
+a.a=l;  a.b=t; a.c=f;
+b.a=m;  b.b=u; b.c=g;
+c.a=n;  c.b=v; c.c=h;
+d.a=o;  d.b=w; d.c=i;
+e.a=p;  e.b=x; e.c=j;
+f.a=q;  f.b=y; f.c=k;
+g.a=r;  g.b=z; g.c=l;
+h.a=s;  h.b=a; h.c=m;
+i.a=t;  i.b=b; i.c=n;
+j.a=u;  j.b=c; j.c=o;
+k.a=v;  k.b=d; k.c=p;
+l.a=w;  l.b=e; l.c=q;
+m.a=x;  m.b=f; m.c=r;
+n.a=y;  n.b=g; n.c=s;
+o.a=z;  o.b=h; o.c=t;
+p.a=a;  p.b=i; p.c=u;
+q.a=b;  q.b=j; q.c=v;
+r.a=c;  r.b=k; r.c=w;
+s.a=d;  s.b=l; s.c=x;
+t.a=e;  t.b=m; t.c=y;
+u.a=f;  u.b=n; u.c=z;
+v.a=g;  v.b=o; v.c=a;
+w.a=h;  w.b=p; w.c=b;
+x.a=i;  x.b=q; x.c=c;
+y.a=j;  y.b=r; y.c=d;
+z.a=k;  z.b=s; z.c=e;
+
+return a.b.c.a.b.c.a.b.c.a.b.c.a.b.c.a.b.c;
+
+""");
+        code.parse().opto().typeCheck().GCM().localSched();
+        assertEquals("return R;", code._stop.toString());
+        assertEquals("R{a=C{a=N{a=Y{a=J{a=U{a=F{a=Q{a=B{a=M{a=X{a=I{a=T{a=E{a=P{a=A{a=L{a=W{a=H{a=S{a=D{a=O{a=Z{a=K{a=V{a=G{a=$cyclic,b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic}", Eval2.eval(code,  0));
+    }
+
 }
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/Chapter13Test.java b/chapter21/src/test/java/com/seaofnodes/simple/Chapter13Test.java
index 6bf45a22..66e12e42 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/Chapter13Test.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/Chapter13Test.java
@@ -1,261 +1,553 @@
 package com.seaofnodes.simple;
-
 import com.seaofnodes.simple.codegen.CodeGen;
+import com.seaofnodes.simple.print.IRPrinter;
+
+
 import org.junit.Test;
 import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.fail;
 
 public class Chapter13Test {
+
+    // A placeholder test used to rapidly rotate through fuzzer produced issues
     @Test
-    public void testJig() {
+    public void testFuzzer() {
         CodeGen code = new CodeGen(
 """
-return 3.14;
+while(---- -arg) {
+    while(-arg) {
+        while(-----arg*---0) {
+                int N=--false==false<--arg;
+                while(N<-4==N) {
+                    N=N+N;
+                }
+            }
+        {
+            int kzEl_r7EYz=3*----0!=-arg<(37*--97!=0/arg==arg)<=-(--arg!=0);
+            while(kzEl_r7EYz<---1) {
+                kzEl_r7EYz=kzEl_r7EYz+kzEl_r7EYz*arg>=24;
+                if(7) continue;
+                kzEl_r7EYz=false;
+                if(-kzEl_r7EYz+arg<-3) continue;
+                else {
+                    while(kzEl_r7EYz) continue;
+                    arg=----3;
+                    kzEl_r7EYz=-(-----arg*1>-kzEl_r7EYz);
+                    int v2uF_4ba=9;
+                }
+            }
+        }
+        int pjcp7rv=arg;
+        {
+            int m2ya3=--arg-pjcp7rv;
+            while(m2ya3<-----pjcp7rv>=pjcp7rv+--pjcp7rv!=---pjcp7rv!=-arg<---(-m2ya3)>m2ya3<=-----true>14!=--m2ya3) {
+                m2ya3=m2ya3+-(--0<=false<pjcp7rv/arg<=-true);
+                while((--m2ya3)<--arg<-----arg*false!=arg<pjcp7rv*arg) {
+                    pjcp7rv=-3+-arg;
+                    break;
+                }
+                while(-3) {
+                    while(67+0-61) m2ya3=m2ya3;
+                    if(----pjcp7rv==---(---arg)) pjcp7rv=0!=-23;
+                    else pjcp7rv=----89;
+                    while(m2ya3!=m2ya3<pjcp7rv) m2ya3=1;
+                    while(--arg<=pjcp7rv) pjcp7rv=-32<=-m2ya3+62;
+                }
+                break;
+            }
+        }
+        {
+            int arg=-1<-9!=(-arg>=-pjcp7rv>=arg<=arg);
+            while(arg<-arg) {
+                arg=arg+--arg;
+                {
+                    while((--93)--pjcp7rv*-pjcp7rv+arg) arg=0-(6>=(--(---41/(0))!=--pjcp7rv)>=---2*33);
+                    pjcp7rv=11;
+                    int c=pjcp7rv;
+                    if(--107) break;
+                    else break;
+                }
+            }
+        }
+        pjcp7rv=pjcp7rv;
+        int aR0Wkua=-pjcp7rv==pjcp7rv;
+        {
+            if(-0!=-0) while(-true) break;
+            else {
+                while(aR0Wkua) pjcp7rv=-0/pjcp7rv;
+                pjcp7rv=pjcp7rv;
+            }
+        }
+    }
+    if(-arg) {
+        {
+            int Isdlt0fr91=0!=arg;
+            while(Isdlt0fr91<-Isdlt0fr91==-Isdlt0fr91+true) {
+                Isdlt0fr91=Isdlt0fr91+-1!=true;
+                if(-arg) if(--arg<=Isdlt0fr91) Isdlt0fr91=-Isdlt0fr91;
+                int i=---arg<---arg!=--40;
+                {
+                    int jVX43Ln4Dm=-(6)==-Isdlt0fr91/----0;
+                    while(jVX43Ln4Dm<--(3-3)) {
+                        jVX43Ln4Dm=jVX43Ln4Dm+-0<25;
+                        i=24<--(jVX43Ln4Dm);
+                    }
+                }
+                i=(arg!=----false>=7);
+                int Te=5>-arg;
+                break;
+            }
+        }
+        arg=arg!=--true/arg;
+        {
+            int UX=arg;
+            while(UX<-3*arg) {
+                UX=UX+arg/-1;
+                arg=-3--(-UX- -47<arg==--arg==arg)/arg- -UX>=-arg;
+                if(---12) while(-UX) break;
+                break;
+            }
+        }
+        continue;
+    }
+    if(arg) arg=--0;
+    else if(1) continue;
+    int DtTlhjYq=19==arg;
+    {
+        arg=--DtTlhjYq<=(DtTlhjYq/---DtTlhjYq<=-DtTlhjYq);
+        if(---arg) continue;
+        else {
+                int Zsl=40;
+                while(Zsl<--Zsl--false>((Zsl))==Zsl!=--DtTlhjYq-DtTlhjYq-DtTlhjYq) {
+                    Zsl=Zsl+arg;
+                }
+            }
+        if((arg)) if(-DtTlhjYq) {
+            }
+            else while(((2)==3*arg/DtTlhjYq)<=0==---arg) return false;
+        else {
+                int lwbF=arg>=0;
+                while(lwbF<57) {
+                    lwbF=lwbF+--(-arg+lwbF)>=-2>=arg!=arg;
+                    arg=----0+0;
+                    while(49) break;
+                    if(true) DtTlhjYq=-----arg;
+                    DtTlhjYq=0!=-----(0);
+                }
+            }
+        arg=---arg!=DtTlhjYq/--0;
+        DtTlhjYq=-DtTlhjYq/(--arg<arg);
+        if(32) {
+                int q=-DtTlhjYq;
+                while(q<arg*(0*q)/0) {
+                    q=q+DtTlhjYq;
+                    DtTlhjYq=arg;
+                }
+            }
+        else if(--arg) if(15) break;
+                else arg=0==arg<=-55>DtTlhjYq;
+            else {
+            }
+        DtTlhjYq=-0;
+        {
+            while((0)<-arg) DtTlhjYq=-DtTlhjYq;
+        }
+        if(30/--(arg)>=0) DtTlhjYq=-0>=arg;
+        else {
+            int Y2wcIQJ=--DtTlhjYq*---11;
+            if(arg==arg) {
+                Y2wcIQJ=-----Y2wcIQJ;
+                Y2wcIQJ=Y2wcIQJ<7;
+                if(DtTlhjYq) arg=arg;
+                else break;
+                while(-arg!=-31==(false<=-15>=-DtTlhjYq+--6*-----Y2wcIQJ<=---arg!=-Y2wcIQJ<=---0<-arg*--Y2wcIQJ)) DtTlhjYq=arg!=3;
+            }
+            continue;
+        }
+        arg=DtTlhjYq;
+        arg=--3/(---arg)>=80>=-DtTlhjYq<=DtTlhjYq;
+        arg=51+---(-true)!=arg!=----1==-DtTlhjYq;
+        if(11<=arg) if((arg)+79<32+(-arg)) continue;
+            else if(true==DtTlhjYq) break;
+        break;
+    }
+}
+if(arg!=62==arg) {
+    while(---arg) {
+        {
+            int bhmDacPM=arg/arg;
+            while(bhmDacPM<arg) {
+                bhmDacPM=bhmDacPM+80*((-bhmDacPM)/---bhmDacPM>1)<bhmDacPM-2!=7;
+                arg=-0;
+                arg=bhmDacPM>=-arg+-arg;
+                break;
+            }
+        }
+        int arg=true;
+        arg=arg<=arg;
+        {
+            int KlC=30;
+            while(KlC<-2) {
+                KlC=KlC+-1!=25<=-KlC>KlC>----0;
+                int Ij=arg>=-arg<=---10;
+                {
+                    int LAbgurVa2R=-arg!=Ij;
+                    while(LAbgurVa2R<-true) {
+                        LAbgurVa2R=LAbgurVa2R+Ij;
+                        KlC=-LAbgurVa2R;
+                        Ij=42*(-Ij>true);
+                        while(Ij) arg=KlC;
+                        KlC=-----7>-(--KlC<--7)==-LAbgurVa2R;
+                    }
+                }
+                int a=Ij<=-KlC;
+                if(Ij) {
+                    int r1W=a!=-false;
+                }
+                else {
+                    arg=56>=Ij;
+                    while(54) break;
+                    arg=8>=-(a<--Ij)/a>=-a-KlC;
+                }
+                int Yt_T=KlC;
+                arg=KlC;
+            }
+        }
+        if(----false/--arg/12+-----0) if(-9+-arg) while(arg!=(arg)) arg=--1>=-71-arg!=---(--arg*11+102)/--arg;
+            else if(----arg) continue;
+        if(-arg-arg) {
+            arg=-(-arg)*--(-3)<(-7==-arg----arg);
+            {
+                int arg=arg;
+                while(arg<-0>arg==-arg-(-arg>1+11)) {
+                    arg=arg+6-arg!=--0>---30>=---arg<=arg/(3)+---arg;
+                }
+            }
+            arg=-arg+arg;
+            arg=--47+-arg<1>arg*(-arg==-arg- -0>3);
+            arg=(----arg)!=arg+--59;
+            arg=- -4+arg==-(arg)-arg;
+        }
+        else {
+            while(--true-----true*-25+-18>arg>=-----(-arg)---13) {
+                arg=-0+--true<false;
+                continue;
+            }
+            arg=true<=arg;
+            break;
+        }
+        arg=arg*22<--(0+-arg);
+        {
+            continue;
+        }
+    }
+    arg=1*---((3<=true)==---2);
+    arg=7+-(-1);
+    return arg+--true;
+}
+else {
+    int o3ypEsewxM=-(---arg);
+    int vzXB=(-(---11<=--o3ypEsewxM>=--0))<=-0/-arg;
+    int L=-arg;
+    int B4mHcrf=---vzXB;
+    int oZWGdzZl=-o3ypEsewxM;
+    int K6tQqa1=11;
+    while(0!=--L) {
+            int sdZfTM=vzXB*true+K6tQqa1;
+            while(sdZfTM<false) {
+                sdZfTM=sdZfTM+arg;
+                sdZfTM=oZWGdzZl;
+                K6tQqa1=-K6tQqa1;
+                arg=---K6tQqa1;
+                while((3+-K6tQqa1)<oZWGdzZl) {
+                    if(-----(-1)) sdZfTM=-false;
+                    {}
+                }
+                K6tQqa1=vzXB!=-(B4mHcrf+-7>false);
+                sdZfTM=vzXB;
+            }
+        }
+    L=false;
+    while(31) B4mHcrf=arg;
+    oZWGdzZl=-0<--oZWGdzZl<=--2;
+    if(K6tQqa1>=20<=46) {
+        if(-1+-L) if(oZWGdzZl) {
+                int wmhv=-----0;
+            }
+        int arg=0;
+        o3ypEsewxM=---(oZWGdzZl);
+        return -oZWGdzZl/0;
+    }
+    else if(arg) {
+            int yKk5=B4mHcrf>=4>K6tQqa1<-B4mHcrf/o3ypEsewxM;
+            return -K6tQqa1;
+        }
+        else {
+            if(---0) {
+                {}
+                {}
+            }
+            return o3ypEsewxM;
+        }
+}
 """);
-        code.parse().opto();
-        assertEquals("return 3.14;", code.print());
-        assertEquals("3.14", Eval2.eval(code,  0));
+        code.parse().opto().typeCheck().GCM();
+        assertEquals("return 9;", code.print());
     }
 
+
     @Test
-    public void testLinkedList0() {
+    public void testPrimes() {
         CodeGen code = new CodeGen(
 """
-struct LLI { LLI? next; int i; };
-LLI? !head = null;
-while( arg ) {
-    LLI !x = new LLI;
-    x.next = head;
-    x.i = arg;
-    head = x;
-    arg = arg-1;
+if( arg < 2 ) return 0;
+int primeCount = 1;
+int prime = 3;
+while( prime <= arg ) {
+    int isPrime = 1;
+    // Check for even case, so the next loop need only check odds
+    if( (prime/2)*2 == prime )
+        continue;
+    // Check odds up to sqrt of prime
+    int j = 3;
+    while( j*j <= prime ) {
+        if( (prime/j)*j == prime ) {
+            isPrime = 0;
+            break;
+        }
+        j = j + 2;
+    }
+    if( isPrime )
+        primeCount = primeCount + 1;
+    prime = prime + 2;
 }
-return head.next.i;
+return primeCount;
 """);
-        try { code.parse().opto().typeCheck(); fail(); }
-        catch( Exception e ) { assertEquals("Might be null accessing 'next'",e.getMessage()); }
+        code.parse().opto();
+        assertEquals("return Phi(Region,0,Phi(Loop,1,Phi(Region,Phi_primeCount,Phi_primeCount,(Phi_primeCount+1))));", code.print());
+        assertEquals("0", Eval2.eval(code,  1)); // No primes 1 or below
+        assertEquals("1", Eval2.eval(code,  2)); // 2
+        assertEquals("2", Eval2.eval(code,  3)); // 2, 3
+        assertEquals("2", Eval2.eval(code,  4)); // 2, 3
+        assertEquals("3", Eval2.eval(code,  5)); // 2, 3, 5
+        assertEquals("4", Eval2.eval(code, 10)); // 2, 3, 5, 7
     }
 
     @Test
-    public void testLinkedList1() {
+    public void testAntiDeps1() {
         CodeGen code = new CodeGen(
 """
-struct LLI { LLI? next; int i; };
-LLI? !head = null;
-while( arg ) {
-    LLI !x = new LLI;
-    x.next = head;
-    x.i = arg;
-    head = x;
-    arg = arg-1;
-}
-if( !head ) return 0;
-LLI? next = head.next;
-if( next==null ) return 1;
-return next.i;
+struct S { int f; };
+!S !v=new S;
+v.f = 2;
+int i=new S.f;
+i=v.f;
+if (arg) v.f=1;
+return i;
 """);
         code.parse().opto();
-        assertEquals("return Phi(Region,0,1,.i);", code.print());
-        assertEquals("2", Eval2.eval(code,  3));
+        assertEquals("return 2;", code.print());
+        assertEquals("2", Eval2.eval(code, 0));
+        assertEquals("2", Eval2.eval(code, 1));
     }
 
     @Test
-    public void testCoRecur() {
+    public void testAntiDeps2() {
         CodeGen code = new CodeGen(
 """
-struct int0 { int i; flt0? f; };
-struct flt0 { flt f; int0? i; };
-int0 !i0 = new int0;
-i0.i = 17;
-flt0 !f0 = new flt0;
-f0.f = 3.14;
-i0.f = f0;
-f0.i = i0;
-return f0.i.f.i.i;
+struct S { int f; };
+!S !v = new S;
+v.f = arg;
+!S !t = new S;
+int i = 0;
+if (arg) {
+    if (arg+1) v = t;
+    i = v.f;
+} else {
+    v.f = 2;
+}
+return i;
 """);
         code.parse().opto();
-        assertEquals("return 17;", code.print());
+        assertEquals("return Phi(Region,.f,0);", code.print());
     }
 
     @Test
-    public void testNullRef0() {
+    public void testAntiDeps3() {
         CodeGen code = new CodeGen(
 """
-struct N { N? next; int i; };
-N n = new N;
-return n.next;
+struct S { int f; };
+!S !v0 = new S;
+!S? !v1;
+if (arg) v1 = new S;
+if (v1) {
+    v0.f = v1.f;
+} else {
+    v0.f = 2;
+}
+return v0;
 """);
         code.parse().opto();
-        assertEquals("return null;", code.print());
+        assertEquals("return S;", code.print());
     }
 
+
     @Test
-    public void testNullRef1() {
+    public void testAntiDeps4() {
         CodeGen code = new CodeGen(
 """
-struct M { int m; };
-struct N { M next; int i; };
-N n = new N { next = new M; };
-return n.next;
+struct S { int f; };
+!S !v = new S;
+v.f = arg;
+S t = new S;
+int i = v.f;
+if (arg+1) arg= 0;
+while (arg) v.f = 2;
+return i;
 """);
         code.parse().opto();
-        assertEquals("return (const)M;", code.print());
+        assertEquals("return arg;", code.print());
     }
 
     @Test
-    public void testNullRef2() {
+    public void testAntiDeps5() {
         CodeGen code = new CodeGen(
 """
-struct M { int m; };
-struct N { M next; int i; };
-N n = new N { next = null; }
-return n.next;
+struct S { int f; };
+!S !v = new S;
+while(1) {
+    while(arg+1) { arg=arg-1; }
+    if (arg) break;
+    v.f = 2;
+}
+return v;
 """);
-        try { code.parse().opto(); fail(); }
-        catch( Exception e ) { assertEquals("Type null is not of declared type *M",e.getMessage()); }
+        code.parse().opto();
+        assertEquals("return S;", code.print());
     }
 
     @Test
-    public void testNullRef3() {
+    public void testAntiDeps6() {
         CodeGen code = new CodeGen(
 """
-struct N { N? next; int i; };
-N !n = new N;
-n.i = 3.14;
-return n.i;
+struct s { int v; };
+!s !ptr=new s;
+while( -arg )
+  ptr = new s;
+while(1)
+  arg = arg+ptr.v;
 """);
-        try { code.parse().opto(); fail(); }
-        catch( Exception e ) { assertEquals("Type 3.14 is not of declared type int",e.getMessage()); }
+        code.parse().opto();
+        assertEquals("return Top;", code.print());
     }
 
     @Test
-    public void testNullRef4() {
-        CodeGen code = new CodeGen("-null-5/null-5;");
-        try { code.parse().opto().typeCheck(); fail(); }
-        catch( Exception e ) { assertEquals("Cannot 'Add' null",e.getMessage()); }
-    }
-
-    @Test public void testNullRef5() {
-        CodeGen code = new CodeGen("return null+42;");
-        try { code.parse().opto().typeCheck(); fail(); }
-        catch( Exception e ) { assertEquals("Cannot 'Add' null",e.getMessage()); }
+    public void testAntiDeps7() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int f; };
+!S !v = new S;
+S t = new S;
+int i = v.f;
+while (arg) {
+    v.f = arg;
+    arg = arg-1;
+}
+return i;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
     }
 
     @Test
-    public void testEmpty() {
+    public void testAntiDeps8() {
         CodeGen code = new CodeGen(
 """
-struct S{};
+struct S { int f; };
+!S !v = new S;
+S t = new S;
+while(arg) {
+    arg=arg-1;
+    int f = v.f;
+    v.f = 2;
+    if (arg) arg = f;
+    else v.f = 3;
+}
+return arg;
 """);
         code.parse().opto();
         assertEquals("return 0;", code.print());
-        assertEquals("0", Eval2.eval(code,  0));
     }
 
     @Test
-    public void testForwardRef0() {
+    public void testAntiDeps9() {
         CodeGen code = new CodeGen(
 """
-struct S1 { S2? s; };
-return new S2;
+struct S { int f; };
+!S !v = new S;
+S t = new S;
+if (arg) {
+    v.f=2;
+    int i=t.f;
+    v.f=i;
+}
+return v;
 """);
-        try { code.parse().opto(); fail(); }
-        catch( Exception e ) { assertEquals("Unknown struct type 'S2'",e.getMessage()); }
+        code.parse().opto();
+        assertEquals("return S;", code.print());
     }
 
     @Test
-    public void testForwardRef1() {
+    public void testExample2() {
         CodeGen code = new CodeGen(
 """
-struct S1 { S2? s; };
-struct S2 { int x; };
-return new S1.s=new S2;
-""");
+struct S { int f; };
+!S !v = new S;
+int i = arg;
+while (arg > 0) {
+    int j = i/3;
+    if (arg == 5)
+        v.f = j;
+    arg = arg - 1;
+}
+return v;
+                """);
         code.parse().opto();
-        assertEquals("return S2;", code.print());
+        //assertEquals("return new S;", code.print());
     }
 
     @Test
-    public void testcheckNull() {
+    public void testScheduleUse() {
         CodeGen code = new CodeGen(
 """
-struct I {int i;};
-struct P { I? pi; };
-P !p1 = new P;
-P !p2 = new P;
-p2.pi = new I;
-p2.pi.i = 2;
-if (arg) p1 = new P;
-return p1.pi.i + 1;
+int v0=0;
+while(0>=0) {
+    u1 v1=0;
+    v1=v0;
+    if(v1*0)
+        v0=-v1;
+}
+return 0;
 """);
-        try { code.parse().opto().typeCheck();  fail(); }
-        catch( Exception e ) {  assertEquals("Might be null accessing 'i'",e.getMessage());  }
+        code.parse().opto();
+        assertEquals("return Top;", code.print());
     }
 
     @Test
-    public void testCoRecur2() {
+    public void testLoopCarriedDep() {
         CodeGen code = new CodeGen(
 """
-struct A { L? a; T? b; F? c; };  A? !a = new A;
-struct B { M? a; U? b; G? c; };  B? !b = new B;
-struct C { N? a; V? b; H? c; };  C? !c = new C;
-struct D { O? a; W? b; I? c; };  D? !d = new D;
-struct E { P? a; X? b; J? c; };  E? !e = new E;
-struct F { Q? a; Y? b; K? c; };  F? !f = new F;
-struct G { R? a; Z? b; L? c; };  G? !g = new G;
-struct H { S? a; A? b; M? c; };  H? !h = new H;
-struct I { T? a; B? b; N? c; };  I? !i = new I;
-struct J { U? a; C? b; O? c; };  J? !j = new J;
-struct K { V? a; D? b; P? c; };  K? !k = new K;
-struct L { W? a; E? b; Q? c; };  L? !l = new L;
-struct M { X? a; F? b; R? c; };  M? !m = new M;
-struct N { Y? a; G? b; S? c; };  N? !n = new N;
-struct O { Z? a; H? b; T? c; };  O? !o = new O;
-struct P { A? a; I? b; U? c; };  P? !p = new P;
-struct Q { B? a; J? b; V? c; };  Q? !q = new Q;
-struct R { C? a; K? b; W? c; };  R? !r = new R;
-struct S { D? a; L? b; X? c; };  S? !s = new S;
-struct T { E? a; M? b; Y? c; };  T? !t = new T;
-struct U { F? a; N? b; Z? c; };  U? !u = new U;
-struct V { G? a; O? b; A? c; };  V? !v = new V;
-struct W { H? a; P? b; B? c; };  W? !w = new W;
-struct X { I? a; Q? b; C? c; };  X? !x = new X;
-struct Y { J? a; R? b; D? c; };  Y? !y = new Y;
-struct Z { K? a; S? b; E? c; };  Z? !z = new Z;
-
-a.a=l;  a.b=t; a.c=f;
-b.a=m;  b.b=u; b.c=g;
-c.a=n;  c.b=v; c.c=h;
-d.a=o;  d.b=w; d.c=i;
-e.a=p;  e.b=x; e.c=j;
-f.a=q;  f.b=y; f.c=k;
-g.a=r;  g.b=z; g.c=l;
-h.a=s;  h.b=a; h.c=m;
-i.a=t;  i.b=b; i.c=n;
-j.a=u;  j.b=c; j.c=o;
-k.a=v;  k.b=d; k.c=p;
-l.a=w;  l.b=e; l.c=q;
-m.a=x;  m.b=f; m.c=r;
-n.a=y;  n.b=g; n.c=s;
-o.a=z;  o.b=h; o.c=t;
-p.a=a;  p.b=i; p.c=u;
-q.a=b;  q.b=j; q.c=v;
-r.a=c;  r.b=k; r.c=w;
-s.a=d;  s.b=l; s.c=x;
-t.a=e;  t.b=m; t.c=y;
-u.a=f;  u.b=n; u.c=z;
-v.a=g;  v.b=o; v.c=a;
-w.a=h;  w.b=p; w.c=b;
-x.a=i;  x.b=q; x.c=c;
-y.a=j;  y.b=r; y.c=d;
-z.a=k;  z.b=s; z.c=e;
-
-return a.b.c.a.b.c.a.b.c.a.b.c.a.b.c.a.b.c;
-
+u32 v0=0;
+{
+    int v1=0;
+    while(v1) {
+        v1=1>>>v0!=0;
+        v0=v1/0;
+    }
+    return v1;
+}
 """);
-        code.parse().opto().typeCheck().GCM().localSched();
-        assertEquals("return R;", code._stop.toString());
-        assertEquals("R{a=C{a=N{a=Y{a=J{a=U{a=F{a=Q{a=B{a=M{a=X{a=I{a=T{a=E{a=P{a=A{a=L{a=W{a=H{a=S{a=D{a=O{a=Z{a=K{a=V{a=G{a=$cyclic,b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic}", Eval2.eval(code,  0));
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
     }
 
 }
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/Chapter14FloatTest.java b/chapter21/src/test/java/com/seaofnodes/simple/Chapter14FloatTest.java
new file mode 100644
index 00000000..009beb0b
--- /dev/null
+++ b/chapter21/src/test/java/com/seaofnodes/simple/Chapter14FloatTest.java
@@ -0,0 +1,82 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.codegen.CodeGen;
+import com.seaofnodes.simple.node.StopNode;
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class Chapter14FloatTest {
+    @Test public void testSubZeroFloat() {
+        var code = new CodeGen("flt x = arg; return 0-x;").parse().opto().typeCheck();
+        // Compare strings so +0.0 and -0.0 remain distinct.
+        assertEquals("0.0", Eval2.eval(code,0));
+        assertEquals("-1.0", Eval2.eval(code,1));
+    }
+
+    @Test public void testDeadNumericReturns() {
+        for( String[] test : new String[][] {
+            {"if(1) return 7; else return 2.5;", "7"},
+            {"if(0) return 7; else return 2.5;", "2.5"},
+            {"return 7; return 2.5;", "7"},
+            {"return 2.5; return 7;", "2.5"}
+        } ) {
+            String src = test[0];
+            var code = new CodeGen(src).parse().opto().typeCheck();
+            assertEquals(src,test[1],Eval2.eval(code,0));
+        }
+    }
+
+
+    @Test
+    public void testJig() {
+        CodeGen code = new CodeGen(
+"""
+return 3.14;
+""");
+        code.parse().opto();
+        assertEquals("return 3.14;", code.print());
+        assertEquals("3.14", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testFloat() {
+        CodeGen code = new CodeGen(
+"""
+return 3.14;
+""");
+        code.parse().opto();
+        assertEquals("return 3.14;", code.print());
+        assertEquals("3.14", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testSquareRoot() {
+        CodeGen code = new CodeGen(
+"""
+flt guess = arg;
+while( 1 ) {
+    flt next = (arg/guess + guess)/2;
+    if( next == guess ) break;
+    guess = next;
+}
+return guess;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,(flt)arg,(((ToFloat/Phi_guess)+Phi_guess)*0.5f));", code.print());
+        assertEquals("3.0", Eval2.eval(code,  9));
+        assertEquals("1.414213562373095", Eval2.eval(code,  2));
+    }
+
+    @Test
+    public void testFPOps() {
+        CodeGen code = new CodeGen(
+"""
+flt x = arg;
+return x+1==x;
+""");
+        code.parse().opto();
+        assertEquals("return ((flt)arg==(ToFloat+1.0f));", code.print());
+        assertEquals("0", Eval2.eval(code, 1));
+    }
+}
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/Chapter14Test.java b/chapter21/src/test/java/com/seaofnodes/simple/Chapter14Test.java
index b83516e3..3a514763 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/Chapter14Test.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/Chapter14Test.java
@@ -93,7 +93,7 @@ return b;
         CodeGen code = new CodeGen(
 """
 struct Foo { u1 b; };
-Foo !f = new Foo;
+!Foo !f = new Foo;
 f.b = 123;
 return f.b;
 """);
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/Chapter15Test.java b/chapter21/src/test/java/com/seaofnodes/simple/Chapter15Test.java
index 8b138b46..94187d1c 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/Chapter15Test.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/Chapter15Test.java
@@ -24,8 +24,8 @@ return 3.14;
     public void testCyclic() {
         CodeGen code = new CodeGen(
 """
-struct C { C? l; };
-C !c = new C;
+struct C { !C? !l; };
+!C !c = new C;
 c.l = c;
 return c;
 """);
@@ -97,7 +97,7 @@ return a[0];
         CodeGen code = new CodeGen(
 """
 struct A { int i; };
-A?[] !a = new A?[2];
+!A?[] !a = new !A?[2];
 return a;
 """);
         code.parse().opto();
@@ -111,16 +111,16 @@ return a;
 """
 struct S { int x; flt y; };
 // A new S
-S !s = new S; s.x=99; s.y = 3.14;
+!S !s = new S; s.x=99; s.y = 3.14;
 
 // Double-d array of Ss.  Fill in one row.
-S?[]?[] !iss = new S?[]?[2];
-iss[0] = new S?[7];
+!S?[]?[] !iss = new !S?[]?[2];
+iss[0] = new !S?[7];
 iss[0][2] = s;
 
 // Now pull out the filled-in value, with null checks
 flt rez;
-S?[]? is = iss[arg];
+!S?[]? is = iss[arg];
 if( !is ) rez = 1.2;
 else {
     S? i = is[2];
@@ -141,11 +141,11 @@ return rez;
 """
 struct S { int x; flt y; };
 // A new S
-S !s = new S; s.x=99; s.y = 3.14;
+!S !s = new S; s.x=99; s.y = 3.14;
 
 // Double-d array of Ss.  Fill in one row.
-S?[]?[] !iss = new S?[]?[2];
-iss[0] = new S?[7];
+!S?[]?[] !iss = new !S?[]?[2];
+iss[0] = new !S?[7];
 iss[0][2] = s;
 
 // Now pull out the filled-in value, with null checks
@@ -166,9 +166,9 @@ return rez;""");
         CodeGen code = new CodeGen(
 """
 // Can we define a forward-reference array?
-struct Tree { Tree?[]? _kids; };
-Tree !root = new Tree;
-root._kids = new Tree?[2]; // NO BANG SO ARRAY IS OF IMMUTABLE TREES????
+struct Tree { !Tree?[]? !_kids; };
+!Tree !root = new Tree;
+root._kids = new !Tree?[2]; // NO BANG SO ARRAY IS OF IMMUTABLE TREES????
 root._kids[0] = new Tree;
 return root;
 """);
@@ -181,7 +181,7 @@ return root;
     public void testNestedStructAddMemProj() {
         CodeGen code = new CodeGen(
 """
-struct S { int a; int[] b; };
+struct S { int a; int[] !b; };
 return 0;
 """);
         code.parse().opto();
@@ -226,8 +226,8 @@ return ary[1] * 1000 + ary[3]; // 1 * 1000 + 6
         CodeGen code = new CodeGen(
 """
 struct S {int i; flt f;};
-S !s1 = new S;
-S !s2 = new S;
+!S !s1 = new S;
+!S !s2 = new S;
 s2.i = 3;
 s2.f = 2.0;
 if (arg) s1 = new S;
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/Chapter16Test.java b/chapter21/src/test/java/com/seaofnodes/simple/Chapter16Test.java
index 571a0d54..884597cf 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/Chapter16Test.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/Chapter16Test.java
@@ -44,31 +44,6 @@ return x+y;
         assertEquals("5", Eval2.eval(code,  0));
     }
 
-//    @Test
-//    public void testFinal0() {
-//        CodeGen code = new CodeGen(
-//"""
-//int !x=2;
-//x=3;
-//return x;
-//""");
-//        try { code.parse().opto(); fail(); }
-//        catch( Exception e ) { assertEquals("Cannot reassign final 'x'",e.getMessage()); }
-//    }
-
-    @Test
-    public void testFinal1() {
-        CodeGen code = new CodeGen(
-"""
-int x=2, y=3;
-if( arg ) { int x = y; x = x*x; y=x; } // Shadow final x
-return y;
-""");
-        code.parse().opto();
-        assertEquals("return Phi(Region,9,3);", code.print());
-        assertEquals("3", Eval2.eval(code, 0));
-        assertEquals("9", Eval2.eval(code, 1));
-    }
 
     @Test
     public void testConstruct0() {
@@ -83,18 +58,6 @@ return z.x;
     }
 
     @Test
-    public void testConstruct1() {
-        CodeGen code = new CodeGen("""
-struct X { int !x; };
-X z = new X { x=3; };
-return z.x;
-""");
-        code.parse().opto();
-        assertEquals("return 3;", code.print());
-        assertEquals("3", Eval2.eval(code,  0));
-    }
-
-    @Test
     public void testConstruct2() {
         CodeGen code = new CodeGen("""
 struct X { int x=3; };
@@ -108,83 +71,11 @@ return z.x;
 
 
     @Test
-    public void testStructFinal0() {
-        CodeGen code = new CodeGen("""
-struct Point { int !x, !y; };
-Point p = new Point { x=3; y=4; };
-return p;
-""");
-        code.parse().opto();
-        assertEquals("return (const)Point;", code.print());
-        assertEquals("Point{x=3,y=4}", Eval2.eval(code,  0));
-    }
-
-    @Test
-    public void testStructFinal1() {
-        CodeGen code = new CodeGen("""
-struct Point { int x=3, y=4; };
-Point p = new Point { x=5; y=6; };
-p.x++;
-return p;
-""");
-        try { code.parse().opto().typeCheck(); fail(); }
-        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
-    }
-
-    @Test
-    public void testStructFinal2() {
-        CodeGen code = new CodeGen("""
-struct Point { int x=3, y=4; };
-Point p = new Point;
-p.x++;
-return p;
-""");
-        try { code.parse().opto().typeCheck(); fail(); }
-        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
-    }
-
-    @Test
-    public void testStructFinal3() {
-        for( String fields : new String[] { "var x; var y;", "int[] x;", "int[] !x;" } ) {
-            String src = "struct Point { "+fields+" }; Point p = new Point; p.x++; return p;";
-            try { new CodeGen(src).parse().opto(); fail(fields); }
-            catch( Exception e ) { assertEquals("'Point' is not fully initialized, field 'x' needs to be set in a constructor",e.getMessage()); }
-        }
-    }
-
-    @Test
-    public void testStructFinal4() {
-        CodeGen code = new CodeGen("""
-struct Point { val x=3; val y=4; };
-Point p = new Point;
-p.x++;
-return p;
-""");
-        try { code.parse().opto(); fail(); }
-        catch( Exception e ) { assertEquals("Cannot reassign final 'x'",e.getMessage()); }
-    }
-
-    @Test
-    public void testStructFinal5() {
-        CodeGen code = new CodeGen("""
-struct Point { var x=3; var y=4; };
-Point !p = new Point;
-p.x++;
-return p;
-""");
-        code.parse().opto();
-        assertEquals("return Point;", code.print());
-        assertEquals("Point{x=4,y=4}", Eval2.eval(code,  0));
-    }
-
-    // Same as the Chapter13 test with the same name, but using the new
-    // constructor syntax
-    @Test
     public void testLinkedList1() {
         CodeGen code = new CodeGen(
 """
-struct LLI { LLI? next; int i; };
-LLI? !head = null;
+struct LLI { !LLI? !next; int i; };
+!LLI? !head = null;
 while( arg ) {
     head = new LLI { next=head; i=arg; };
     arg = arg-1;
@@ -205,8 +96,8 @@ return next.i;
     public void testLinkedList2() {
         CodeGen code = new CodeGen(
 """
-struct LLI { LLI? next; int i; };
-LLI? !head = null;
+struct LLI { !LLI? !next; int i; };
+!LLI? !head = null;
 while( arg ) {
     head = new LLI {
         next=head;
@@ -258,13 +149,13 @@ return new Square;
     static final String CONSTRUCTOR_MEMORY = """
         struct S { int x; int y; };
         struct T { int z=arg+40; };
-        T !t = new T;
-        S !a = new S { x=11; y=7; };
-        S !b = new S { x=22; y=9; };
-        S !p=a;
+        !T !t = new T;
+        !S !a = new S { x=11; y=7; };
+        !S !b = new S { x=22; y=9; };
+        !S !p=a;
         if (arg) p=b;
         int before=p.x;
-        S !c = new S {
+        !S !c = new S {
             x=p.x+1;
             { int i=0; while (i<2) { p.y=p.y+1; i=i+1; } }
             y=p.y;
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/Chapter17aTest.java b/chapter21/src/test/java/com/seaofnodes/simple/Chapter17aTest.java
new file mode 100644
index 00000000..16ffe967
--- /dev/null
+++ b/chapter21/src/test/java/com/seaofnodes/simple/Chapter17aTest.java
@@ -0,0 +1,108 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.codegen.CodeGen;
+import com.seaofnodes.simple.evaluator.Evaluator;
+import com.seaofnodes.simple.node.StopNode;
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class Chapter17aTest {
+
+    @Test
+    public void testFinal1() {
+        CodeGen code = new CodeGen(
+"""
+int x=2, y=3;
+if( arg ) { int x = y; x = x*x; y=x; } // Shadow final x
+return y;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,9,3);", code.print());
+        assertEquals("3", Eval2.eval(code, 0));
+        assertEquals("9", Eval2.eval(code, 1));
+    }
+
+    @Test
+    public void testConstruct1() {
+        CodeGen code = new CodeGen("""
+struct X { int ~x; };
+X z = new X { x=3; };
+return z.x;
+""");
+        code.parse().opto();
+        assertEquals("return 3;", code.print());
+        assertEquals("3", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testStructFinal0() {
+        CodeGen code = new CodeGen("""
+struct Point { int ~x, ~y; };
+Point p = new Point { x=3; y=4; };
+return p;
+""");
+        code.parse().opto();
+        assertEquals("return (const)Point;", code.print());
+        assertEquals("Point{x=3,y=4}", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testStructFinal1() {
+        CodeGen code = new CodeGen("""
+struct Point { int x=3, y=4; };
+Point p = new Point { x=5; y=6; };
+p.x++;
+return p;
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
+    }
+
+    @Test
+    public void testStructFinal2() {
+        CodeGen code = new CodeGen("""
+struct Point { int x=3, y=4; };
+Point p = new Point;
+p.x++;
+return p;
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
+    }
+
+    @Test
+    public void testStructFinal3() {
+        for( String fields : new String[] { "var x; var y;", "int[] !x;", "int[] !x;" } ) {
+            String src = "struct Point { "+fields+" }; Point p = new Point; p.x++; return p;";
+            try { new CodeGen(src).parse().opto(); fail(fields); }
+            catch( Exception e ) { assertEquals("'Point' is not fully initialized, field 'x' needs to be set in a constructor",e.getMessage()); }
+        }
+    }
+
+    @Test
+    public void testStructFinal4() {
+        CodeGen code = new CodeGen("""
+struct Point { val x=3; val y=4; };
+Point p = new Point;
+p.x++;
+return p;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot reassign final 'x'",e.getMessage()); }
+    }
+
+    @Test
+    public void testStructFinal5() {
+        CodeGen code = new CodeGen("""
+struct Point { var x=3; var y=4; };
+!Point !p = new Point;
+p.x++;
+return p;
+""");
+        code.parse().opto();
+        assertEquals("return Point;", code.print());
+        assertEquals("Point{x=4,y=4}", Eval2.eval(code,  0));
+    }
+
+}
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/Chapter17Test.java b/chapter21/src/test/java/com/seaofnodes/simple/Chapter17bTest.java
index 5de4ec3c..eeb94d50 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/Chapter17Test.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/Chapter17bTest.java
@@ -5,7 +5,7 @@ import org.junit.Test;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.fail;
 
-public class Chapter17Test {
+public class Chapter17bTest {
 
     @Test
     public void testJig() {
@@ -80,7 +80,7 @@ return xs[0];
     public void testInc5() {
         CodeGen code = new CodeGen("""
 struct S { u16 x; };
-S !s = new S;
+!S !s = new S;
 s.x--;
 return s.x;
 """);
@@ -156,14 +156,14 @@ return s.x;
     }
 
     @Test public void testVar4() {
-        CodeGen code = new CodeGen("struct S{int x;}; S? s; s=new S; s.x++; return s.x; // Ok, no initializer so x is mutable ");
+        CodeGen code = new CodeGen("struct S{int x;}; !S? !s; s=new S; s.x++; return s.x; // Ok, no initializer so x is mutable ");
         code.parse().opto();
         assertEquals("return 1;", code.print());
         assertEquals("1", Eval2.eval(code, 0));
     }
 
     @Test public void testVar5() {
-        CodeGen code = new CodeGen("struct S{int x;}; S? s; s=new S{x=3;}; s.x++; return s.x; // Ok, no initializer so x is mutable ");
+        CodeGen code = new CodeGen("struct S{int x;}; !S? !s; s=new S{x=3;}; s.x++; return s.x; // Ok, no initializer so x is mutable ");
         code.parse().opto();
         assertEquals("return 4;", code.print());
         assertEquals("4", Eval2.eval(code, 0));
@@ -182,7 +182,7 @@ return s.x;
     }
 
     @Test public void testVar8() {
-        CodeGen code = new CodeGen("struct S{int x;}; S !s=new S; s.x++; return s.x; // Ok, has '!' so s.x is mutable ");
+        CodeGen code = new CodeGen("struct S{int x;}; !S !s=new S; s.x++; return s.x; // Ok, has '!' so s.x is mutable ");
         code.parse().opto();
         assertEquals("return 1;", code.print());
         assertEquals("1", Eval2.eval(code, 0));
@@ -196,7 +196,7 @@ return s.x;
     }
 
     @Test public void testVar10() {
-        CodeGen code = new CodeGen("struct S{int x;}; val s=new S; s.x++; return s.x; // Error, has val so x is immutable ");
+        CodeGen code = new CodeGen("struct S{int x;}; ~S s=new S; s.x++; return s.x; // Error, has val so x is immutable ");
         try { code.parse().opto().typeCheck(); fail(); }
         catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
     }
@@ -204,15 +204,15 @@ return s.x;
     @Test public void testVar11() {
         CodeGen code = new CodeGen("""
 struct Bar { int x; };
-Bar !bar = new Bar;
+!Bar !bar = new Bar;
 bar.x = 3; // Ok, bar is mutable
 
-struct Foo { Bar? !bar; int y; };
-Foo !foo = new Foo { bar = bar; };
+struct Foo { !Bar? !bar; int y; };
+!Foo !foo = new Foo { bar = bar; };
 foo.bar = bar; // Ok foo is mutable
 foo.bar.x++;   // Ok foo and foo.bar and foo.bar.x are all mutable
 
-val xfoo = foo; // Throw away mutability
+~Foo xfoo = foo; // Throw away mutability
 xfoo.bar.x++;   // Error, cannot mutate through xfoo
  """);
         try { code.parse().opto().typeCheck(); fail(); }
@@ -222,15 +222,15 @@ xfoo.bar.x++;   // Error, cannot mutate through xfoo
     @Test public void testVar12() {
         CodeGen code = new CodeGen("""
 struct Bar { int x; };
-Bar !bar = new Bar;
+!Bar !bar = new Bar;
 bar.x = 3; // Ok, bar is mutable
 
-struct Foo { Bar? !bar; int y; };
-Foo !foo = new Foo;
+struct Foo { !Bar? !bar; int y; };
+!Foo !foo = new Foo;
 foo.bar = bar; // Ok bar is mutable
 foo.bar.x++;   // Ok foo and foo.bar and foo.bar.x are all mutable
 
-val xfoo = foo;        // Throw away mutability
+~Foo xfoo = foo;        // Throw away mutability
 int x4 = xfoo.bar.x;   // Ok to read through xfoo, gets 4
 foo.bar.x++;           // Bumps to 5
 int x5 = xfoo.bar.x;   // Ok to read through xfoo, gets 5
@@ -255,7 +255,7 @@ int i,i++;
     public void testVar14() {
         CodeGen code = new CodeGen("""
 struct B {};
-struct A { B b; };
+struct A { !B !b; };
 A x = new A {
     return b; // read before init
     b = new B;
@@ -269,7 +269,7 @@ A x = new A {
     public void testVar15() {
         CodeGen code = new CodeGen("""
 struct B {};
-struct A { B b; };
+struct A { !B !b; };
 return new A {
     if (arg) b = new B; // Constructor ends with partial init of b
 }.b;
@@ -299,10 +299,10 @@ return x;
 struct Person {
     bool focused;
 };
-val focus = { Person p ->
+val focus = { !Person p ->
     p.focused = true;
 };
-Person me; // Person !me = new Person;
+!Person !me; // !Person !me = new Person;
 focus(me);
 return me;
 """
@@ -363,7 +363,7 @@ return b ? b.x++ + b.x++ : -1;
     public void testTrinary4() {
         // This test case will benefit from an unzipping transformation
         CodeGen code = new CodeGen("""
-struct Bar { Bar? next; int x; };
+struct Bar { !Bar? !next; int x; };
 var b = arg ? new Bar { next = (arg==2) ? new Bar{x=2;}; x=1; };
 return b ? b.next ? b.next.x : b.x; // parses "b ? (b.next ? b.next.x : b.x) : 0"
 """);
@@ -478,8 +478,8 @@ for(;;arg++;) {}
     public void testForward0() {
         CodeGen code = new CodeGen("""
 struct A{
-    B? f1;
-    B? f2;
+    !B? !f1;
+    !B? !f2;
 };
 return new A;
 """);
@@ -492,13 +492,13 @@ return new A;
     public void testForward1() {
         CodeGen code = new CodeGen("""
 struct A{
-    B?[]? nil_array_of_b;
-    B?[]  not_array_of_b = new B?[0];
+    !B?[]? !nil_array_of_b;
+    !B?[]  not_array_of_b = new !B?[0];
 };
 return new A.not_array_of_b;
 """);
         code.parse().opto();
-        assertEquals("return (const)[*B?];", code.print());
+        assertEquals("return [*B?];", code.print());
         assertEquals("*B?[]", Eval2.eval(code,0));
     }
 
@@ -506,8 +506,8 @@ return new A.not_array_of_b;
     @Test
     public void testLinkedList2() {
         CodeGen code = new CodeGen("""
-struct LLI { LLI? next; int i; };
-LLI? !head = null;
+struct LLI { !LLI? !next; int i; };
+!LLI? !head = null;
 while( arg-- )
     head = new LLI { next=head; i=arg; };
 int sum=0;
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/Chapter18Test.java b/chapter21/src/test/java/com/seaofnodes/simple/Chapter18Test.java
index 89aae28e..173fb653 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/Chapter18Test.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/Chapter18Test.java
@@ -272,7 +272,7 @@ return 2;
     public void testFcn8() {
         CodeGen code = new CodeGen(
 """
-{int -> int}? i2i = null;
+{int -> int}? !i2i = null;
 var id = {{int->int} f-> return f;};
 for(;;) {
     if (i2i) return i2i(arg);
@@ -290,7 +290,7 @@ for(;;) {
     public void testFcn9() {
         CodeGen code = new CodeGen(
 """
-{int -> int}? i2i = null;
+{int -> int}? !i2i = null;
 for(;;) {
     if (i2i) return i2i(arg);
     var x = {int i-> return i;};
@@ -311,13 +311,13 @@ struct Person {
   int age;
 };
 
-val fcn = { Person?[] ps, int x ->
+val fcn = { !Person?[] !ps, int x ->
   val tmp = ps[x];
   if( ps[x] )
     ps[x].age++;
 };
 
-var ps = new Person?[2];
+var ps = new !Person?[2];
 ps[0] = new Person;
 ps[1] = new Person;
 fcn(ps,1);
@@ -381,7 +381,7 @@ struct S {
     {int} f = { -> x(); return 0; }; // Do not let fref x be a field
 };
 val x = { -> return 1; };
-S? s = null;
+!S? !s = null;
 for(;;) {
     if (s) return s.x;
 }
@@ -430,7 +430,7 @@ struct S {
     { int } f = { -> return x(); };
 };
 val x = { -> return 1; };
-S? s = null;
+!S? !s = null;
 for(;;) {
     if (s) return s.f;
 }
@@ -464,7 +464,7 @@ return f2f(o)(1);
 struct Person {
     int coffee_count;
 };
-Person !p = new Person;
+!Person !p = new Person;
 p.coffee_count += 1;
 return p.coffee_count;
 """);
@@ -475,10 +475,10 @@ return p.coffee_count;
 
     static final String CALL_MEMORY = """
         struct S { int x; int y; };
-        val bump = { S s, int d -> int old=s.x; s.x=old+d; return old; };
-        S !a = new S { x=10; y=7; };
-        S !b = new S { x=20; y=9; };
-        S !p=a; if (arg) p=b;
+        val bump = { !S !s, int d -> int old=s.x; s.x=old+d; return old; };
+        !S !a = new S { x=10; y=7; };
+        !S !b = new S { x=20; y=9; };
+        !S !p=a; if (arg) p=b;
         int before=p.x;
         int old=bump(p,3);
         int after=p.x;
@@ -504,13 +504,13 @@ return p.coffee_count;
 
     static final String RECURSIVE_MEMORY = """
         struct S { int x; };
-        val rec = { S s, int n ->
+        val rec = { !S !s, int n ->
             if (n==0) return s.x;
             int before=s.x;
             s.x=before+1;
             return before+rec(s,n-1);
         };
-        S !s=new S { x=10; };
+        !S !s=new S { x=10; };
         int value=rec(s,arg);
         return value*100+s.x;
         """;
@@ -523,12 +523,12 @@ return p.coffee_count;
 
     static final String INLINE_MEMORY = """
         struct S { int x; int y; };
-        val make = { S s ->
+        val make = { !S s ->
             S t = new S { x=s.x+1; y=3; };
             s.y=9;
             return t;
         };
-        S !a = new S { x=arg+40; y=7; };
+        !S !a = new S { x=arg+40; y=7; };
         S t=make(a);
         return a.x*10000+a.y*100+t.x+t.y;
         """;
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/Chapter19Test.java b/chapter21/src/test/java/com/seaofnodes/simple/Chapter19Test.java
index 1149c518..c230e615 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/Chapter19Test.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/Chapter19Test.java
@@ -225,7 +225,7 @@ return sum;""");
     public void testAlloc1() {
         CodeGen code = new CodeGen(
 """
-struct S { int a; S? c; };
+struct S { int a; !S? !c; };
 return new S;""");
         code.driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         assertEquals("return S;", code.print());
@@ -398,8 +398,8 @@ return sq(arg) + sq(3);
     @Test public void testFoldedReadBeforeWrites() {
         var code = new CodeGen("""
             struct S { int x; };
-            S !a = new S { x=11; }; S !b = new S { x=22; };
-            S !p = a; if( arg ) p = b;
+            !S !a = new S { x=11; }; !S !b = new S { x=22; };
+            !S !p = a; if( arg ) p = b;
             int before = p.x + arg;
             a.x=33; b.x=44;
             return before;
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/Chapter20Test.java b/chapter21/src/test/java/com/seaofnodes/simple/Chapter20Test.java
index 3dc95ab9..be945a0b 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/Chapter20Test.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/Chapter20Test.java
@@ -16,7 +16,7 @@ public class Chapter20Test {
             // A real integer return merged with a synthetic exit.
             "if(arg) while(1) {} return arg+1;",
             // TOP must not widen a non-null pointer or constrain a float register.
-            "struct S { int x; }; S !s=new S; if(arg) while(1) {} return s;",
+            "struct S { int x; }; !S !s=new S; if(arg) while(1) {} return s;",
             "if(arg) while(1) {} return 1.5;",
             // Several synthetic exits into the same return.
             "if(arg==1) while(1) {} if(arg==2) while(1) {} return arg+3;",
@@ -24,7 +24,7 @@ public class Chapter20Test {
             "while(1) { arg+=1; }",
             "if(arg) while(1) {} while(1) {}",
             // Loop-carried memory and scalar self-conflicts exercise spilling.
-            "struct S { int x; int y; }; S !a=new S; if(arg) while(1) { a.x+=arg; a.y+=a.x; } return a.x+a.y;"
+            "struct S { int x; int y; }; !S !a=new S; if(arg) while(1) { a.x+=arg; a.y+=a.x; } return a.x+a.y;"
         };
         for( String target : new String[]{"x86_64_v2","riscv","arm"} )
             for( String src : sources ) {
@@ -45,7 +45,7 @@ public class Chapter20Test {
 
     @Test public void testNarrowStoreMasks() {
         for( String type : new String[]{"i8","u8","i16","u16"} ) {
-            CodeGen code = new CodeGen("struct S { "+type+" x; }; S !s=new S; s.x=arg; return 0;")
+            CodeGen code = new CodeGen("struct S { "+type+" x; }; !S !s=new S; s.x=arg; return 0;")
                 .driver(CodeGen.Phase.RegAlloc,"x86_64_v2","SystemV");
             int stores=0;
             for( var bb : code._cfg )
@@ -61,9 +61,9 @@ public class Chapter20Test {
     @Test public void testInlinedReturnValue() {
         String src = """
 struct S { int x; };
-val f = { S s -> s.x = g(); };
+val f = { !S s -> s.x = g(); };
 val g = { -> 123; };
-S !s = new S;
+!S !s = new S;
 return f(s);
 """;
         // The entry of g can disappear before its Return is folded into f.
@@ -201,11 +201,11 @@ return ary[1] * 1000 + ary[3]; // 1 * 1000 + 6
     public void testString() {
         String src = """
 struct String {
-    u8[] cs;
+    u8[] !cs;
     int _hashCode;
 };
 
-val equals = { String self, String s ->
+val equals = { !String !self, !String s ->
     if( self == s ) return true;
     if( self.cs# != s.cs# ) return false;
     for( int i=0; i< self.cs#; i++ )
@@ -214,13 +214,13 @@ val equals = { String self, String s ->
     return true;
 };
 
-val hashCode = { String self ->
+val hashCode = { !String self ->
     self._hashCode
     ?  self._hashCode
     : (self._hashCode = _hashCodeString(self));
 };
 
-val _hashCodeString = { String self ->
+val _hashCodeString = { !String self ->
     int hash=0;
     if( self.cs ) {
         for( int i=0; i< self.cs#; i++ )
@@ -230,7 +230,7 @@ val _hashCodeString = { String self ->
     return hash;
 };
 
-String !s = new String { cs = new u8[17]; };
+!String !s = new String { cs = new u8[17]; };
 s.cs[0] =  67; // C
 s.cs[1] = 108; // l
 hashCode(s);
@@ -349,12 +349,12 @@ return output;
 """
 // based on the top-down version from https://en.wikipedia.org/wiki/Merge_sort
 
-val merge_sort = { int[] a, int[] b, int n ->
+val merge_sort = { int[] !a, int[] !b, int n ->
     copy_array(a, 0, n, b);
     split_merge(a, 0, n, b);
 };
 
-val split_merge = { int[] b, int begin, int end, int[] a ->
+val split_merge = { int[] !b, int begin, int end, int[] a ->
     if (end - begin <= 1)
         return 0;
     int middle = (end + begin) / 2;
@@ -364,7 +364,7 @@ val split_merge = { int[] b, int begin, int end, int[] a ->
     return 0;
 };
 
-val merge = { int[] b, int begin, int middle, int end, int[] a ->
+val merge = { int[] !b, int begin, int middle, int end, int[] a ->
     int i = begin, j = middle;
 
     for (int k = begin; k < end; k++) {
@@ -379,7 +379,7 @@ val merge = { int[] b, int begin, int middle, int end, int[] a ->
     }
 };
 
-val copy_array = { int[] a, int begin, int end, int[] b ->
+val copy_array = { int[] !a, int begin, int end, int[] b ->
     for (int k = begin; k < end; k++)
         b[k] = a[k];
 };
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/Chapter21Test.java b/chapter21/src/test/java/com/seaofnodes/simple/Chapter21Test.java
index f431feeb..f9a6b4fc 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/Chapter21Test.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/Chapter21Test.java
@@ -18,8 +18,8 @@ public class Chapter21Test {
 
     @Test public void testReadBeforeConditionalStore() {
         var code = new CodeGen("""
-            struct S { int x; }; S !a=new S; S !b=new S;
-            a.x=10; b.x=20; S !p=a; if(arg&1) p=b;
+            struct S { int x; }; !S !a=new S; !S !b=new S;
+            a.x=10; b.x=20; !S !p=a; if(arg&1) p=b;
             int sum=0;
             for(int i=0; i<6; i++) {
                 sum+=a.x;
@@ -105,7 +105,7 @@ public class Chapter21Test {
 
     @Test public void testNarrowStores() throws IOException {
         for( String type : new String[]{"i8","u8","i16","u16"} ) {
-            String src = "struct S { "+type+" x; }; S !s = new S; s.x = arg; return 0;";
+            String src = "struct S { "+type+" x; }; !S !s = new S; s.x = arg; return 0;";
             CodeGen code = new CodeGen(src).driver("riscv","SystemV",null);
             int stores=0;
             for( var bb : code._cfg )
@@ -295,7 +295,7 @@ public class Chapter21Test {
     }
 
     @Test public void testInfinite() {
-        String src = "struct S { int i; }; S !s = new S; while(1) s.i++;";
+        String src = "struct S { int i; }; !S !s = new S; while(1) s.i++;";
         testCPU(src,"x86_64_v2", "SystemV",0,"return Top;");
         testCPU(src,"riscv"    , "SystemV",2,"return Top;");
         testCPU(src,"arm"      , "SystemV",2,"return Top;");
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/CompoundAssignmentTest.java b/chapter21/src/test/java/com/seaofnodes/simple/CompoundAssignmentTest.java
index 0d67d3c5..48f739cf 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/CompoundAssignmentTest.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/CompoundAssignmentTest.java
@@ -73,7 +73,7 @@ public class CompoundAssignmentTest {
     @Test public void testFields() {
         for (String op : OPS) {
             long expected = apply(op, -8, 3);
-            check("struct S { int x; }; S !s=new S; s.x=arg; int r=(s.x " +
+            check("struct S { int x; }; !S !s=new S; s.x=arg; int r=(s.x " +
                   op + " 3); return s.x*10+r;", -8, expected*11);
         }
     }
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/MemoryEncodingTest.java b/chapter21/src/test/java/com/seaofnodes/simple/MemoryEncodingTest.java
index 3ad7c4cb..f0a68402 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/MemoryEncodingTest.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/MemoryEncodingTest.java
@@ -31,8 +31,8 @@ public class MemoryEncodingTest {
             """,
             // One possibly aliasing arm must reject the unchanged-memory proof.
             """
-            struct S { int x; }; S !a=new S; S !b=new S;
-            a.x=10; b.x=20; S !p=a; if(arg&1) p=b;
+            struct S { int x; }; !S !a=new S; !S !b=new S;
+            a.x=10; b.x=20; !S !p=a; if(arg&1) p=b;
             int sum=0;
             for(int i=0; i<6; i++) {
                 if(i==2) p.x=30;
@@ -43,8 +43,8 @@ public class MemoryEncodingTest {
             """,
             // Unchanged memory does not imply an unchanged loop-carried pointer.
             """
-            struct S { int x; }; S !a=new S; S !b=new S;
-            a.x=10; b.x=20; S !p=a; int sum=0;
+            struct S { int x; }; !S !a=new S; !S !b=new S;
+            a.x=10; b.x=20; !S !p=a; int sum=0;
             for(int i=0; i<6; i++) {
                 if(i==2) a.x=30;
                 sum+=p.x;
@@ -54,7 +54,7 @@ public class MemoryEncodingTest {
             """,
             // All arms fold, but their values differ: build a value Phi.
             """
-            struct S { int x; }; S !a=new S; a.x=1; int sum=0;
+            struct S { int x; }; !S !a=new S; a.x=1; int sum=0;
             for(int i=0; i<6; i++) {
                 sum+=a.x;
                 if(i&1) a.x=2;
@@ -145,7 +145,7 @@ public class MemoryEncodingTest {
         for( String target : new String[]{"x86_64_v2","riscv","arm"} ) {
             CodeGen code = new CodeGen("""
                 struct S { int x; int y; };
-                S !a=new S;
+                !S !a=new S;
                 if( arg ) while( 1 ) { a.x+=arg; a.y+=a.x; }
                 return a.x+a.y;
                 """).driver(CodeGen.Phase.LoopTree);
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/MutabilityTest.java b/chapter21/src/test/java/com/seaofnodes/simple/MutabilityTest.java
new file mode 100644
index 00000000..7ae80314
--- /dev/null
+++ b/chapter21/src/test/java/com/seaofnodes/simple/MutabilityTest.java
@@ -0,0 +1,73 @@
+package com.seaofnodes.simple;
+
+import org.junit.Test;
+import static org.junit.Assert.*;
+import com.seaofnodes.simple.codegen.CodeGen;
+
+public class MutabilityTest {
+    private static void ok(String src, String result) {
+        var code = new CodeGen(src).parse().opto().typeCheck();
+        assertEquals(result,Eval2.eval(code,0));
+    }
+    private static void bad(String src) {
+        try {
+            new CodeGen(src).parse().opto().typeCheck();
+        } catch( RuntimeException expected ) {
+            String msg = expected.getMessage();
+            assertTrue("Expected a permission error, got: "+expected,
+                msg!=null && (msg.contains("final") || msg.contains("not of declared type") || msg.contains("Cannot store") || msg.contains("Argument #")));
+            return;
+        }
+        fail("Accepted forbidden write: "+src);
+    }
+
+    @Test public void testIndependentBindingsAndViews() {
+        ok("struct P { int x; }; !P ~p=new P; p.x=7; return p.x;", "7");
+        ok("struct P { int x; }; ~P !p=new P{x=3;}; p=new P{x=7;}; return p.x;", "7");
+        bad("struct P { int x; }; !P ~p=new P; p=new P; return 0;");
+        bad("struct P { int x; }; ~P !p=new P; p.x=7; return 0;");
+        bad("int ~x=3; x=7; return x;");
+        ok("int !x=3; x=7; return x;", "7");
+    }
+
+    @Test public void testDeepViewAndAliases() {
+        ok("struct P { int x; }; !P ~p=new P; ~P ~r=p; p.x=7; return r.x;", "7");
+        bad("struct P { int x; }; struct Box { !P p; }; !P q=new P; Box b=new Box{p=q;}; b.p.x=7; return 0;");
+        bad("struct P { int x; }; P p=new P; !P q=p; q.x=7; return 0;");
+        bad("struct P { P? next; int x; }; !P p=new P{next=new P;}; p.next.x=7; return 0;");
+        bad("struct P { !P? next; int x; }; P p=new P{next=new P;}; p.next.x=7; return 0;");
+    }
+
+    @Test public void testInferencePreservesAccess() {
+        ok("struct P { int x; }; val p=new P; p.x=7; return p.x;", "7");
+        bad("struct P { int x; }; val p=new P; p=new P; return 0;");
+        bad("struct P { int x; }; P p=new P; var q=p; q.x=7; return 0;");
+    }
+
+    @Test public void testParameterPermissions() {
+        ok("struct P { int x; }; val f={ !P p -> p.x=7; return p.x; }; return f(new P);", "7");
+        ok("val f={ int ~x -> return x; }; return f(7);", "7");
+        bad("val f={ int ~x -> x=7; return x; }; return f(3);");
+        bad("struct P { int x; }; val f={ P p -> p.x=7; return p.x; }; return f(new P);");
+        bad("struct P { int x; }; val f={ !P p -> p.x=7; return p.x; }; P p=new P; return f(p);");
+        bad("struct P { int x; }; val f={ P?[] a -> return a#; }; !P?[] a=new !P?[1]; return f(a);");
+    }
+
+    @Test public void testConstructorScope() {
+        ok("struct P { int ~x; }; P p=new P{if(arg) x=3; else x=7;}; return p.x;", "7");
+        bad("int ~outer=1; struct P { int x; }; P p=new P{outer=7;}; return outer;");
+        bad("struct P { int x; }; P p=new P{int ~local=1; local=7;}; return p.x;");
+    }
+
+    @Test public void testArrayLayers() {
+        bad("struct P { int x; }; !P?[] rw=new !P?[1]; P?[] ro=rw; rw[0]=new P; ro[0].x=7; return 0;");
+        ok("u8[] a=new u8[2]; a[0]=7; return a[0];", "7");
+        ok("struct P { int x; }; P?[] a=new P?[1]; a[0]=new P{x=7;}; return a[0].x;", "7");
+        bad("struct P { int x; }; P?[] a=new P?[1]; a[0]=new P; a[0].x=7; return 0;");
+        ok("struct P { int x; }; !P?[] a=new !P?[1]; a[0]=new P; a[0].x=7; return a[0].x;", "7");
+        bad("u8[~] a=new u8[1]; a[0]=7; return 0;");
+        ok("u8[~]?[] rows=new u8[~]?[1]; rows[0]=new u8[1]; return rows#;", "1");
+        bad("u8[~]?[] rows=new u8[~]?[1]; rows[0]=new u8[1]; rows[0][0]=7; return 0;");
+        bad("u8[]?[~] rows=new u8[]?[1]; rows[0]=new u8[1]; return 0;");
+    }
+}
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/SchedulerTest.java b/chapter21/src/test/java/com/seaofnodes/simple/SchedulerTest.java
index ca29bf84..3b19857a 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/SchedulerTest.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/SchedulerTest.java
@@ -25,7 +25,7 @@ public class SchedulerTest {
 struct S {
     int f;
 }
-S !v=new S;
+!S !v=new S;
 v.f = 2;
 int i=v.f;
 if (arg) v.f=1;
@@ -42,7 +42,7 @@ return i;
 struct S {
     int f;
 };
-S !v0=new S;
+!S !v0=new S;
 if(arg) v0.f=1;
 return v0;
 """);
@@ -58,7 +58,7 @@ return v0;
 struct S {
     int f;
 };
-S !v=new S;
+!S !v=new S;
 v.f = 2;
 int i=new S.f;
 i=v.f;
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/TypeTest.java b/chapter21/src/test/java/com/seaofnodes/simple/TypeTest.java
index d94f5b5a..dee033bc 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/TypeTest.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/TypeTest.java
@@ -56,12 +56,12 @@ public class TypeTest {
 
         Assert.assertNotEquals(ptr1, ptr2);
         Assert.assertNotEquals(ptr1, ptr1.glb());
-        Assert.assertEquals(ptr1nil.makeRO(), ptr1.glb());
+        Assert.assertEquals(ptr1nil.makeFrom(s1.glb()).makeRO(), ptr1.glb());
 
         Assert.assertEquals(ptr1, ptr1.dual().dual());
-        Assert.assertEquals(ptr1.glb().makeRO(), ptr1.dual().glb());
-        Assert.assertEquals(TypeMemPtr.makeNullable(TypeStruct.BOT), ptr1.meet(ptr2nil));
-        Assert.assertEquals(ptr1.glb(), ptr1.meet(TypeNil.NIL).makeRO());
+        Assert.assertEquals(ptr1.glb().makeFrom(s1.dual().glb()), ptr1.dual().glb());
+        Assert.assertEquals(TypeMemPtr.makeNullable(TypeStruct.BOT).withAccess(false), ptr1.meet(ptr2nil));
+        Assert.assertEquals(ptr1nil, ptr1.meet(TypeNil.NIL));
 
         TypeMemPtr TOP = TypeMemPtr.TOP;
         TypeMemPtr BOT = TypeMemPtr.makeNullable(TypeStruct.BOT);
@@ -70,7 +70,7 @@ public class TypeTest {
         Type PTR_meet_NULL = NULL.meet(PTR);
         Assert.assertEquals(BOT, PTR_meet_NULL);
         Type ptr1_meet_ptr2 = ptr1.meet(ptr2);
-        Assert.assertEquals(PTR, ptr1_meet_ptr2);
+        Assert.assertEquals(PTR.withAccess(false), ptr1_meet_ptr2);
         Type NULL_join_ptr1 = NULL.join(ptr1);
         Assert.assertEquals(TypePtr.XNPTR, NULL_join_ptr1);
         Type NULL_join_PTR = PTR.join(NULL);
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/fuzzer/ScriptGenerator.java b/chapter21/src/test/java/com/seaofnodes/simple/fuzzer/ScriptGenerator.java
index f119fa1a..167a5b24 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/fuzzer/ScriptGenerator.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/fuzzer/ScriptGenerator.java
@@ -467,7 +467,7 @@ public class ScriptGenerator {
         for (int i=0; i<fields.length; i++) {
             var fieldName = getRandomName();
             var type = getType(true);
-            printIndentation().append(type.name).append(" ").append(fieldName).append(";\n");
+            printIndentation().append(declType(type)).append(" !").append(fieldName).append(";\n");
             fields[i] = new TypeStruct.Field(fieldName.toString(), type, struct);
         }
         indentation -= INDENTATION;
@@ -664,15 +664,17 @@ public class ScriptGenerator {
         return 0;
     }
 
-    /**
-     * Generate a declaration statement.
-     * @return 0
-     */
+    // This generator mutates references and fields; request both permissions.
+    private static String declType(Type type) {
+        return (type instanceof TypeStruct || type instanceof TypeNullable ? "!" : "") + type.name;
+    }
+
+    /** Generate a declaration statement. */
     public int genDecl() {
         var type = getType();
         var name = getVarName();
         // Always make them mutable
-        sb.append(generateInvalid() ? getRandomName() : type.name).append(" !").append(name);
+        sb.append(generateInvalid() ? getRandomName() : declType(type)).append(" !").append(name);
         if (!(type instanceof TypeNullable) || random.nextBoolean()) {
             sb.append("=");
             genExpression(type, true);
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/progs/antiDep1.smp b/chapter21/src/test/java/com/seaofnodes/simple/progs/antiDep1.smp
index b18dfd16..52bfe29b 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/progs/antiDep1.smp
+++ b/chapter21/src/test/java/com/seaofnodes/simple/progs/antiDep1.smp
@@ -1,7 +1,7 @@
 // -*- mode: java;  -*-
 struct S { int f; };
 var v0 = new S;
-S? v1;
+!S? !v1;
 if (arg) v1 = new S;
 if (v1) {
     v0.f = v1.f;
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/progs/person.smp b/chapter21/src/test/java/com/seaofnodes/simple/progs/person.smp
index 9f0f5bea..b5e6ee90 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/progs/person.smp
+++ b/chapter21/src/test/java/com/seaofnodes/simple/progs/person.smp
@@ -3,7 +3,7 @@ struct Person {
     int age;
 };
 
-val fcn = { Person?[] ps, int x ->
+val fcn = { !Person?[] ps, int x ->
     if( ps[x] )
         ps[x].age++;
 };
\ No newline at end of file
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/progs/stringHash.smp b/chapter21/src/test/java/com/seaofnodes/simple/progs/stringHash.smp
index dafa7456..257f79f9 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/progs/stringHash.smp
+++ b/chapter21/src/test/java/com/seaofnodes/simple/progs/stringHash.smp
@@ -5,7 +5,7 @@ struct String {
 };
 
 // Compare two Strings
-val equals = { String self, String s ->
+val equals = { !String !self, !String s ->
     if( self == s ) return true;
     if( self.cs# != s.cs# ) return false;
     for( int i=0; i< self.cs#; i++ )
@@ -15,13 +15,13 @@ val equals = { String self, String s ->
 };
 
 // Return the String hashCode (cached, and never 0)
-val hashCode = { String self ->
+val hashCode = { !String self ->
     self._hashCode
     ?  self._hashCode
     : (self._hashCode = _hashCodeString(self));
 };
 
-val _hashCodeString = { String self ->
+val _hashCodeString = { !String self ->
     int hash=0;
     if( self.cs )
         for( int i=0; i< self.cs#; i++ )