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

22 files changed, 1128 insertions, 1054 deletions

diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter10Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter10Test.java
index 7da1354f..91505f41 100644
--- a/chapter20/src/test/java/com/seaofnodes/simple/Chapter10Test.java
+++ b/chapter20/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/chapter20/src/test/java/com/seaofnodes/simple/Chapter10bTest.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter10bTest.java
deleted file mode 100644
index 5d78ae06..00000000
--- a/chapter20/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/chapter20/src/test/java/com/seaofnodes/simple/Chapter11Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter11Test.java
index 71449197..a38e93c1 100644
--- a/chapter20/src/test/java/com/seaofnodes/simple/Chapter11Test.java
+++ b/chapter20/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 Phi(Region,9,Top,Top,Top,Top);", 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(Region,(Phi_primeCount+1),Phi_primeCount))));", 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/chapter20/src/test/java/com/seaofnodes/simple/Chapter12Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter12Test.java
index c50be559..36a1a0aa 100644
--- a/chapter20/src/test/java/com/seaofnodes/simple/Chapter12Test.java
+++ b/chapter20/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 'i'",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/chapter20/src/test/java/com/seaofnodes/simple/Chapter13Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter13Test.java
index 977595cb..975946da 100644
--- a/chapter20/src/test/java/com/seaofnodes/simple/Chapter13Test.java
+++ b/chapter20/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 Phi(Region,9,Top,Top,Top,Top);", 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 'i'",e.getMessage()); }
+        code.parse().opto();
+        assertEquals("return Phi(Region,0,Phi(Loop,1,Phi(Region,Phi_primeCount,Phi(Region,(Phi_primeCount+1),Phi_primeCount))));", 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/chapter20/src/test/java/com/seaofnodes/simple/Chapter14FloatTest.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter14FloatTest.java
new file mode 100644
index 00000000..009beb0b
--- /dev/null
+++ b/chapter20/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/chapter20/src/test/java/com/seaofnodes/simple/Chapter14Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter14Test.java
index b83516e3..3a514763 100644
--- a/chapter20/src/test/java/com/seaofnodes/simple/Chapter14Test.java
+++ b/chapter20/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/chapter20/src/test/java/com/seaofnodes/simple/Chapter15Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter15Test.java
index 7dd0710a..73014399 100644
--- a/chapter20/src/test/java/com/seaofnodes/simple/Chapter15Test.java
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter15Test.java
@@ -21,8 +21,8 @@ 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;
 """);
@@ -94,7 +94,7 @@ 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();
@@ -108,16 +108,16 @@ 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];
@@ -138,11 +138,11 @@ 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
@@ -163,9 +163,9 @@ 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;
 """);
@@ -178,7 +178,7 @@ 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();
@@ -255,8 +255,8 @@ return rez;
         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/chapter20/src/test/java/com/seaofnodes/simple/Chapter16Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter16Test.java
index 571a0d54..884597cf 100644
--- a/chapter20/src/test/java/com/seaofnodes/simple/Chapter16Test.java
+++ b/chapter20/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/chapter20/src/test/java/com/seaofnodes/simple/Chapter17aTest.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter17aTest.java
new file mode 100644
index 00000000..16ffe967
--- /dev/null
+++ b/chapter20/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/chapter20/src/test/java/com/seaofnodes/simple/Chapter17Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter17bTest.java
index 6e43dbc8..b799ee82 100644
--- a/chapter20/src/test/java/com/seaofnodes/simple/Chapter17Test.java
+++ b/chapter20/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/chapter20/src/test/java/com/seaofnodes/simple/Chapter18Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter18Test.java
index 75b18cf3..b5cc0682 100644
--- a/chapter20/src/test/java/com/seaofnodes/simple/Chapter18Test.java
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter18Test.java
@@ -281,7 +281,7 @@ 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);
@@ -299,7 +299,7 @@ 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;};
@@ -320,13 +320,13 @@ 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);
@@ -390,7 +390,7 @@ 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;
 }
@@ -439,7 +439,7 @@ struct S {
     { int } f = { -> return x(); };
 };
 val x = { -> return 1; };
-S? s = null;
+!S? !s = null;
 for(;;) {
     if (s) return s.f;
 }
@@ -473,7 +473,7 @@ 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;
 """);
@@ -484,10 +484,10 @@ 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;
@@ -513,13 +513,13 @@ 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;
         """;
@@ -532,12 +532,12 @@ 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/chapter20/src/test/java/com/seaofnodes/simple/Chapter19Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter19Test.java
index a7321c96..f7329e63 100644
--- a/chapter20/src/test/java/com/seaofnodes/simple/Chapter19Test.java
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter19Test.java
@@ -47,11 +47,11 @@ return 0;
         CodeGen code = new CodeGen(
 """
 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++ )
@@ -60,13 +60,13 @@ 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++ )
@@ -76,7 +76,7 @@ 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)+hashCode(s);""");
@@ -259,7 +259,7 @@ 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.parse().opto().typeCheck().instSelect(PORTS,"x86_64_v2", "SystemV").GCM().localSched();
         assertEquals("return S;", code.print());
@@ -466,8 +466,8 @@ 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/chapter20/src/test/java/com/seaofnodes/simple/Chapter20Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter20Test.java
index 19854767..5a7375f5 100644
--- a/chapter20/src/test/java/com/seaofnodes/simple/Chapter20Test.java
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter20Test.java
@@ -16,7 +16,7 @@ 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;")
                 .parse().opto().typeCheck().instSelect(PORTS,"x86_64_v2","SystemV").GCM().localSched().regAlloc();
             int stores=0;
             for( var bb : code._cfg )
@@ -32,9 +32,9 @@ 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.
@@ -168,11 +168,11 @@ 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++ )
@@ -181,13 +181,13 @@ 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++ )
@@ -197,7 +197,7 @@ 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);
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/CompoundAssignmentTest.java b/chapter20/src/test/java/com/seaofnodes/simple/CompoundAssignmentTest.java
index 0d67d3c5..48f739cf 100644
--- a/chapter20/src/test/java/com/seaofnodes/simple/CompoundAssignmentTest.java
+++ b/chapter20/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/chapter20/src/test/java/com/seaofnodes/simple/MergeSortTest.java b/chapter20/src/test/java/com/seaofnodes/simple/MergeSortTest.java
index c83fe089..31fbe3a4 100644
--- a/chapter20/src/test/java/com/seaofnodes/simple/MergeSortTest.java
+++ b/chapter20/src/test/java/com/seaofnodes/simple/MergeSortTest.java
@@ -13,12 +13,12 @@ public class MergeSortTest {
 """
 // 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;
@@ -28,7 +28,7 @@ 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++) {
@@ -43,7 +43,7 @@ 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/chapter20/src/test/java/com/seaofnodes/simple/MutabilityTest.java b/chapter20/src/test/java/com/seaofnodes/simple/MutabilityTest.java
new file mode 100644
index 00000000..7ae80314
--- /dev/null
+++ b/chapter20/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/chapter20/src/test/java/com/seaofnodes/simple/SchedulerTest.java b/chapter20/src/test/java/com/seaofnodes/simple/SchedulerTest.java
index ca29bf84..3b19857a 100644
--- a/chapter20/src/test/java/com/seaofnodes/simple/SchedulerTest.java
+++ b/chapter20/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/chapter20/src/test/java/com/seaofnodes/simple/TypeTest.java b/chapter20/src/test/java/com/seaofnodes/simple/TypeTest.java
index d94f5b5a..dee033bc 100644
--- a/chapter20/src/test/java/com/seaofnodes/simple/TypeTest.java
+++ b/chapter20/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/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/ScriptGenerator.java b/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/ScriptGenerator.java
index f119fa1a..167a5b24 100644
--- a/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/ScriptGenerator.java
+++ b/chapter20/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/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn.smp b/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn.smp
index 188e0a9f..43d398b3 100644
--- a/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn.smp
+++ b/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn.smp
@@ -3,13 +3,13 @@ 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++;
 };
 
-Person?[] !ps = new Person?[2];
+!Person?[] !ps = new !Person?[2];
 ps[0] = new Person;
 ps[1] = new Person;
 fcn(ps,1);
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn3.smp b/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn3.smp
index a64564f0..55b74455 100644
--- a/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn3.smp
+++ b/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn3.smp
@@ -1,6 +1,6 @@
 
 //val fact = { int n -> n <= 1 ? 1 : fact(n-1)*n; }
-struct LL { LL? next; int payload; };
+struct LL { !LL? !next; int payload; };
 
 
 struct String {
@@ -13,7 +13,7 @@ struct String {
         return hash;
     };
 
-    val equals = { String s ->
+    val equals = { !String s ->
         if( self == s ) return true;
         if( cs# != s.cs# ) return false;
         for( int i=0; i< #; i++ )
@@ -28,7 +28,7 @@ struct String {
 
 
 
-val hashCode= { String self ->
+val hashCode= { !String self ->
     int hash = self._hashCode
     ? self._hashCode
     : self._hashCode = _hashCodeString(self);