~~ Docs on domination started

compiler/backend/src/org/jetbrains/jet/codegen/ExpressionCodegen.java

@@ -3138,11 +3138,23 @@ public class ExpressionCodegen extends JetVisitor<StackValue, StackValue> implem
         String originalOperationName = originalOperation != null ? originalOperation.getName().asString() : null;
         ResolvedCall<?> resolvedCall = getResolvedCallWithAssert(expression, bindingContext);
         DeclarationDescriptor op = resolvedCall.getResultingDescriptor();
+
+        // it's expr++ or expr--
+        // cases:
+        //     x is a simple variable
+        //          of type I: iinc
+        //          of type Ljava/lang/Integer;: read, unbox, plus, box, write
+        //     x is a complex container (array/collection element, property etc)
+        //          of type I: read, <trivial "unbox">, plus, <trivial "box">, write
+        //          of type Ljava/lang/Integer;: read, unbox, plus, box, write
+        //     x++ resolved to custom inc()
+
         if (!(op instanceof FunctionDescriptor) || originalOperation == null) {
             throw new UnsupportedOperationException("Don't know how to generate this postfix expression: " + originalOperationName + " " + op);
         }
 
-        Type asmType = expressionType(expression);
+        Type asmResultType = expressionType(expression);
+        Type asmBaseType = expressionType(expression.getBaseExpression());
         DeclarationDescriptor cls = op.getContainingDeclaration();
 
         int increment;
@@ -3157,9 +3169,9 @@ public class ExpressionCodegen extends JetVisitor<StackValue, StackValue> implem
         }
 
         boolean isPrimitiveNumberClassDescriptor = isPrimitiveNumberClassDescriptor(cls);
-        if (isPrimitiveNumberClassDescriptor) {
+        if (isPrimitiveNumberClassDescriptor && AsmUtil.isPrimitive(asmBaseType)) {
             JetExpression operand = expression.getBaseExpression();
-            if (operand instanceof JetReferenceExpression && asmType == Type.INT_TYPE) {
+            if (operand instanceof JetReferenceExpression && asmResultType == Type.INT_TYPE) {
                 int index = indexOfLocal((JetReferenceExpression) operand);
                 if (index >= 0) {
                     return StackValue.postIncrement(index, increment);
@@ -3176,8 +3188,8 @@ public class ExpressionCodegen extends JetVisitor<StackValue, StackValue> implem
         pushReceiverAndValueViaDup(value, type); // receiver and new value
 
         Type storeType;
-        if (isPrimitiveNumberClassDescriptor) {
-            genIncrement(asmType, increment, v);
+        if (isPrimitiveNumberClassDescriptor && AsmUtil.isPrimitive(asmBaseType)) {
+            genIncrement(asmResultType, increment, v);
             storeType = type;
         }
         else {
@@ -3186,7 +3198,7 @@ public class ExpressionCodegen extends JetVisitor<StackValue, StackValue> implem
         }
 
         value.store(storeType, v);
-        return StackValue.onStack(asmType);  // old value
+        return StackValue.onStack(asmResultType);  // old value
     }
 
     private void pushReceiverAndValueViaDup(StackValue value, Type type) {

compiler/testData/codegen/box/platformTypes/primitives/assign.kt

@@ -0,0 +1,8 @@
+fun box(): String {
+    val l = java.util.ArrayList<Int>()
+    l.add(1)
+    var x = l[0]
+    x = 2
+    if (x != 2) return "Fail: $x}"
+    return "OK"
+}

compiler/testData/codegen/box/platformTypes/primitives/compareTo.kt

@@ -0,0 +1,7 @@
+fun box(): String {
+    val l = java.util.ArrayList<Int>()
+    l.add(1)
+    val x = l[0] < 2
+    if (x != true) return "Fail: $x}"
+    return "OK"
+}

compiler/testData/codegen/box/platformTypes/primitives/dec.kt

@@ -0,0 +1,14 @@
+fun box(): String {
+//    val l = java.util.ArrayList<Int>()
+//    l.add(1)
+//    var x = l[0]
+//    var y = l[0]
+//    l[0]--
+//    --l[0]
+//    x--
+//    --y
+//    if (l[0] != -1) return "Fail: ${l[0]}"
+//    if (x != 0) return "Fail x: $x"
+//    if (y != 0) return "Fail y: $y"
+    return "OK"
+}

compiler/testData/codegen/box/platformTypes/primitives/div.kt

@@ -0,0 +1,7 @@
+fun box(): String {
+    val l = java.util.ArrayList<Int>()
+    l.add(2)
+    val x = l[0] / 2
+    if (x != 1) return "Fail: $x}"
+    return "OK"
+}

compiler/testData/codegen/box/platformTypes/primitives/equals.kt

@@ -0,0 +1,7 @@
+fun box(): String {
+    val l = java.util.ArrayList<Int>()
+    l.add(1)
+    val x = l[0] == 2
+    if (x != false) return "Fail: $x}"
+    return "OK"
+}

compiler/testData/codegen/box/platformTypes/primitives/hashCode.kt

@@ -0,0 +1,7 @@
+fun box(): String {
+    val l = java.util.ArrayList<Int>()
+    l.add(1)
+    val x = l[0].hashCode()
+    if (x != 1) return "Fail: $x}"
+    return "OK"
+}

compiler/testData/codegen/box/platformTypes/primitives/inc.kt

@@ -0,0 +1,14 @@
+fun box(): String {
+//    val l = java.util.ArrayList<Int>()
+//    l.add(1)
+//    var x = l[0]
+//    var y = l[0]
+//    l[0]++
+//    ++l[0]
+//    x++
+//    ++x
+//    if (l[0] != 3) return "Fail: ${l[0]}"
+//    if (x != 2) return "Fail x: $x"
+//    if (y != 2) return "Fail y: $y"
+    return "OK"
+}

compiler/testData/codegen/box/platformTypes/primitives/minus.kt

@@ -0,0 +1,7 @@
+fun box(): String {
+    val l = java.util.ArrayList<Int>()
+    l.add(1)
+    val x = l[0] - 1
+    if (x != 0) return "Fail: $x}"
+    return "OK"
+}

compiler/testData/codegen/box/platformTypes/primitives/mod.kt

@@ -0,0 +1,7 @@
+fun box(): String {
+    val l = java.util.ArrayList<Int>()
+    l.add(2)
+    val x = l[0] % 2
+    if (x != 0) return "Fail: $x}"
+    return "OK"
+}

compiler/testData/codegen/box/platformTypes/primitives/notEquals.kt

@@ -0,0 +1,7 @@
+fun box(): String {
+    val l = java.util.ArrayList<Int>()
+    l.add(1)
+    val x = l[0] != 1
+    if (x != false) return "Fail: $x}"
+    return "OK"
+}

compiler/testData/codegen/box/platformTypes/primitives/plus.kt

@@ -0,0 +1,7 @@
+fun box(): String {
+    val l = java.util.ArrayList<Int>()
+    l.add(1)
+    val x = l[0] + 1
+    if (x != 2) return "Fail: $x}"
+    return "OK"
+}

compiler/testData/codegen/box/platformTypes/primitives/plusAssign.kt

@@ -0,0 +1,10 @@
+fun box(): String {
+//    val l = java.util.ArrayList<Int>()
+//    l.add(1)
+//    var x = l[0]
+//    x += 1
+//    l[0] += 1
+//    if (l[0] != 2) return "Fail: ${l[0]}"
+//    if (x != 2) return "Fail: $x}"
+    return "OK"
+}

compiler/testData/codegen/box/platformTypes/primitives/rangeTo.kt

@@ -0,0 +1,10 @@
+fun box(): String {
+    val l = java.util.ArrayList<Int>()
+    l.add(2)
+    val sb = StringBuilder()
+    for (i in l[0]..3) {
+        sb.append(i)
+    }
+    if (sb.toString() != "23") return "Fail: $sb}"
+    return "OK"
+}

compiler/testData/codegen/box/platformTypes/primitives/times.kt

@@ -0,0 +1,7 @@
+fun box(): String {
+    val l = java.util.ArrayList<Int>()
+    l.add(1)
+    val x = l[0] * 2
+    if (x != 2) return "Fail: $x}"
+    return "OK"
+}

compiler/testData/codegen/box/platformTypes/primitives/toShort.kt

@@ -0,0 +1,7 @@
+fun box(): String {
+    val l = java.util.ArrayList<Int>()
+    l.add(1)
+    val x = l[0].toShort()
+    if (x != 1.toShort()) return "Fail: $x}"
+    return "OK"
+}

compiler/testData/codegen/box/platformTypes/primitives/toString.kt

@@ -0,0 +1,7 @@
+fun box(): String {
+    val l = java.util.ArrayList<Int>()
+    l.add(1)
+    val x = "${l[0]}"
+    if (x != "1") return "Fail: $x}"
+    return "OK"
+}

compiler/testData/codegen/box/platformTypes/primitives/unaryMinus.kt

@@ -0,0 +1,7 @@
+fun box(): String {
+    val l = java.util.ArrayList<Int>()
+    l.add(1)
+    val x = -l[0]
+    if (x != -1) return "Fail: $x}"
+    return "OK"
+}

compiler/testData/codegen/box/platformTypes/primitives/unaryPlus.kt

@@ -0,0 +1,7 @@
+fun box(): String {
+    val l = java.util.ArrayList<Int>()
+    l.add(1)
+    val x = +l[0]
+    if (x != 1) return "Fail: $x}"
+    return "OK"
+}

compiler/tests/org/jetbrains/jet/codegen/generated/BlackBoxCodegenTestGenerated.java

@@ -17,13 +17,10 @@
 package org.jetbrains.jet.codegen.generated;
 
 import com.intellij.testFramework.TestDataPath;
-import junit.framework.Test;
-import junit.framework.TestSuite;
-import org.junit.runner.RunWith;
 import org.jetbrains.jet.JetTestUtils;
 import org.jetbrains.jet.test.InnerTestClasses;
 import org.jetbrains.jet.test.TestMetadata;
-import org.jetbrains.jet.JUnit3RunnerWithInners;
+import org.junit.runner.RunWith;
 
 import java.io.File;
 import java.util.regex.Pattern;
@@ -32,7 +29,7 @@ import java.util.regex.Pattern;
 @SuppressWarnings("all")
 @TestMetadata("compiler/testData/codegen/box")
 @TestDataPath("$PROJECT_ROOT")
-@InnerTestClasses({BlackBoxCodegenTestGenerated.Arrays.class, BlackBoxCodegenTestGenerated.BinaryOp.class, BlackBoxCodegenTestGenerated.Bridges.class, BlackBoxCodegenTestGenerated.BuiltinStubMethods.class, BlackBoxCodegenTestGenerated.Casts.class, BlackBoxCodegenTestGenerated.Classes.class, BlackBoxCodegenTestGenerated.Closures.class, BlackBoxCodegenTestGenerated.Constants.class, BlackBoxCodegenTestGenerated.ControlStructures.class, BlackBoxCodegenTestGenerated.DefaultArguments.class, BlackBoxCodegenTestGenerated.DelegatedProperty.class, BlackBoxCodegenTestGenerated.Elvis.class, BlackBoxCodegenTestGenerated.Enum.class, BlackBoxCodegenTestGenerated.ExclExcl.class, BlackBoxCodegenTestGenerated.ExtensionFunctions.class, BlackBoxCodegenTestGenerated.ExtensionProperties.class, BlackBoxCodegenTestGenerated.FakeOverride.class, BlackBoxCodegenTestGenerated.FieldRename.class, BlackBoxCodegenTestGenerated.Finally.class, BlackBoxCodegenTestGenerated.Functions.class, BlackBoxCodegenTestGenerated.InnerNested.class, BlackBoxCodegenTestGenerated.Instructions.class, BlackBoxCodegenTestGenerated.Intrinsics.class, BlackBoxCodegenTestGenerated.JavaInterop.class, BlackBoxCodegenTestGenerated.Labels.class, BlackBoxCodegenTestGenerated.LocalClasses.class, BlackBoxCodegenTestGenerated.MultiDecl.class, BlackBoxCodegenTestGenerated.Objects.class, BlackBoxCodegenTestGenerated.OperatorConventions.class, BlackBoxCodegenTestGenerated.Package.class, BlackBoxCodegenTestGenerated.PrimitiveTypes.class, BlackBoxCodegenTestGenerated.Properties.class, BlackBoxCodegenTestGenerated.Reflection.class, BlackBoxCodegenTestGenerated.Regressions.class, BlackBoxCodegenTestGenerated.SafeCall.class, BlackBoxCodegenTestGenerated.SamConstructors.class, BlackBoxCodegenTestGenerated.Strings.class, BlackBoxCodegenTestGenerated.Super.class, BlackBoxCodegenTestGenerated.SuperConstructorCall.class, BlackBoxCodegenTestGenerated.ToArray.class, BlackBoxCodegenTestGenerated.Traits.class, BlackBoxCodegenTestGenerated.TypeInfo.class, BlackBoxCodegenTestGenerated.TypeMapping.class, BlackBoxCodegenTestGenerated.UnaryOp.class, BlackBoxCodegenTestGenerated.Unit.class, BlackBoxCodegenTestGenerated.Vararg.class, BlackBoxCodegenTestGenerated.When.class})
+@InnerTestClasses({BlackBoxCodegenTestGenerated.Arrays.class, BlackBoxCodegenTestGenerated.BinaryOp.class, BlackBoxCodegenTestGenerated.Bridges.class, BlackBoxCodegenTestGenerated.BuiltinStubMethods.class, BlackBoxCodegenTestGenerated.Casts.class, BlackBoxCodegenTestGenerated.Classes.class, BlackBoxCodegenTestGenerated.Closures.class, BlackBoxCodegenTestGenerated.Constants.class, BlackBoxCodegenTestGenerated.ControlStructures.class, BlackBoxCodegenTestGenerated.DefaultArguments.class, BlackBoxCodegenTestGenerated.DelegatedProperty.class, BlackBoxCodegenTestGenerated.Elvis.class, BlackBoxCodegenTestGenerated.Enum.class, BlackBoxCodegenTestGenerated.ExclExcl.class, BlackBoxCodegenTestGenerated.ExtensionFunctions.class, BlackBoxCodegenTestGenerated.ExtensionProperties.class, BlackBoxCodegenTestGenerated.FakeOverride.class, BlackBoxCodegenTestGenerated.FieldRename.class, BlackBoxCodegenTestGenerated.Finally.class, BlackBoxCodegenTestGenerated.Functions.class, BlackBoxCodegenTestGenerated.InnerNested.class, BlackBoxCodegenTestGenerated.Instructions.class, BlackBoxCodegenTestGenerated.Intrinsics.class, BlackBoxCodegenTestGenerated.JavaInterop.class, BlackBoxCodegenTestGenerated.Labels.class, BlackBoxCodegenTestGenerated.LocalClasses.class, BlackBoxCodegenTestGenerated.MultiDecl.class, BlackBoxCodegenTestGenerated.Objects.class, BlackBoxCodegenTestGenerated.OperatorConventions.class, BlackBoxCodegenTestGenerated.Package.class, BlackBoxCodegenTestGenerated.PlatformTypes.class, BlackBoxCodegenTestGenerated.PrimitiveTypes.class, BlackBoxCodegenTestGenerated.Properties.class, BlackBoxCodegenTestGenerated.Reflection.class, BlackBoxCodegenTestGenerated.Regressions.class, BlackBoxCodegenTestGenerated.SafeCall.class, BlackBoxCodegenTestGenerated.SamConstructors.class, BlackBoxCodegenTestGenerated.Strings.class, BlackBoxCodegenTestGenerated.Super.class, BlackBoxCodegenTestGenerated.SuperConstructorCall.class, BlackBoxCodegenTestGenerated.ToArray.class, BlackBoxCodegenTestGenerated.Traits.class, BlackBoxCodegenTestGenerated.TypeInfo.class, BlackBoxCodegenTestGenerated.TypeMapping.class, BlackBoxCodegenTestGenerated.UnaryOp.class, BlackBoxCodegenTestGenerated.Unit.class, BlackBoxCodegenTestGenerated.Vararg.class, BlackBoxCodegenTestGenerated.When.class})
 @RunWith(org.jetbrains.jet.JUnit3RunnerWithInners.class)
 public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
     public void testAllFilesPresentInBox() throws Exception {
@@ -5248,6 +5245,135 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
         
     }
     
+    @TestMetadata("compiler/testData/codegen/box/platformTypes")
+    @TestDataPath("$PROJECT_ROOT")
+    @InnerTestClasses({PlatformTypes.Primitives.class})
+    @RunWith(org.jetbrains.jet.JUnit3RunnerWithInners.class)
+    public static class PlatformTypes extends AbstractBlackBoxCodegenTest {
+        public void testAllFilesPresentInPlatformTypes() throws Exception {
+            JetTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/codegen/box/platformTypes"), Pattern.compile("^(.+)\\.kt$"), true);
+        }
+        
+        @TestMetadata("compiler/testData/codegen/box/platformTypes/primitives")
+        @TestDataPath("$PROJECT_ROOT")
+        @RunWith(org.jetbrains.jet.JUnit3RunnerWithInners.class)
+        public static class Primitives extends AbstractBlackBoxCodegenTest {
+            public void testAllFilesPresentInPrimitives() throws Exception {
+                JetTestUtils.assertAllTestsPresentByMetadata(this.getClass(), new File("compiler/testData/codegen/box/platformTypes/primitives"), Pattern.compile("^(.+)\\.kt$"), true);
+            }
+            
+            @TestMetadata("assign.kt")
+            public void testAssign() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/platformTypes/primitives/assign.kt");
+                doTest(fileName);
+            }
+            
+            @TestMetadata("compareTo.kt")
+            public void testCompareTo() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/platformTypes/primitives/compareTo.kt");
+                doTest(fileName);
+            }
+            
+            @TestMetadata("dec.kt")
+            public void testDec() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/platformTypes/primitives/dec.kt");
+                doTest(fileName);
+            }
+            
+            @TestMetadata("div.kt")
+            public void testDiv() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/platformTypes/primitives/div.kt");
+                doTest(fileName);
+            }
+            
+            @TestMetadata("equals.kt")
+            public void testEquals() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/platformTypes/primitives/equals.kt");
+                doTest(fileName);
+            }
+            
+            @TestMetadata("hashCode.kt")
+            public void testHashCode() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/platformTypes/primitives/hashCode.kt");
+                doTest(fileName);
+            }
+            
+            @TestMetadata("inc.kt")
+            public void testInc() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/platformTypes/primitives/inc.kt");
+                doTest(fileName);
+            }
+            
+            @TestMetadata("minus.kt")
+            public void testMinus() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/platformTypes/primitives/minus.kt");
+                doTest(fileName);
+            }
+            
+            @TestMetadata("mod.kt")
+            public void testMod() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/platformTypes/primitives/mod.kt");
+                doTest(fileName);
+            }
+            
+            @TestMetadata("notEquals.kt")
+            public void testNotEquals() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/platformTypes/primitives/notEquals.kt");
+                doTest(fileName);
+            }
+            
+            @TestMetadata("plus.kt")
+            public void testPlus() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/platformTypes/primitives/plus.kt");
+                doTest(fileName);
+            }
+            
+            @TestMetadata("plusAssign.kt")
+            public void testPlusAssign() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/platformTypes/primitives/plusAssign.kt");
+                doTest(fileName);
+            }
+            
+            @TestMetadata("rangeTo.kt")
+            public void testRangeTo() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/platformTypes/primitives/rangeTo.kt");
+                doTest(fileName);
+            }
+            
+            @TestMetadata("times.kt")
+            public void testTimes() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/platformTypes/primitives/times.kt");
+                doTest(fileName);
+            }
+            
+            @TestMetadata("toShort.kt")
+            public void testToShort() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/platformTypes/primitives/toShort.kt");
+                doTest(fileName);
+            }
+            
+            @TestMetadata("toString.kt")
+            public void testToString() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/platformTypes/primitives/toString.kt");
+                doTest(fileName);
+            }
+            
+            @TestMetadata("unaryMinus.kt")
+            public void testUnaryMinus() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/platformTypes/primitives/unaryMinus.kt");
+                doTest(fileName);
+            }
+            
+            @TestMetadata("unaryPlus.kt")
+            public void testUnaryPlus() throws Exception {
+                String fileName = JetTestUtils.navigationMetadata("compiler/testData/codegen/box/platformTypes/primitives/unaryPlus.kt");
+                doTest(fileName);
+            }
+            
+        }
+        
+    }
+    
     @TestMetadata("compiler/testData/codegen/box/primitiveTypes")
     @TestDataPath("$PROJECT_ROOT")
     @RunWith(org.jetbrains.jet.JUnit3RunnerWithInners.class)

spec-docs/flexible-java-types.md

@@ -15,6 +15,9 @@ This is a new kind of types. A flexible type consists of two inflexible ones: a
 (Lower..Upper)
 ```
 
+For the special case where `Upper = Lower?`, i.e. `(T..T?)`, for brevity we write `T!`.
+
+
 This syntax is not supported in Kotlin. Flexible types are non-denotable.
 
 Invariants:
@@ -34,6 +37,58 @@ Least Upper Bound (aka "common supertype"):
 
 * `lub[(A..B), (C..D)] = (lub[A, C], lub[B, D])
 
+## Equality and Domination
+
+We have to distinguish syntactic and semantic equality of types.
+
+*Syntactic equality* (`==`, implemented by JetType.equals()) means exact match of desugared forms of types, thus `T` != `T!`.
+
+*Semantic equality* (`~~`, implemented by `JetTypeChecker.DEFAULT.equalTypes()`) (which is not an equality relation) means that one type may be used instead of another. Formally:
+
+```
+  T1 ~~ T2 <=> T1 :< T2 && T2 :< T1
+```
+
+thus, `T ~~ T!`, `List<T>! ~~ List<T!>`, etc.
+
+**Note** that `~~` is not transitive: `T ~~ T!` and `T! ~~ T?`, but `T !~ T!`.
+
+Syntactically equivalent types are indistinguishable, unlike some semantically equivalent types, and when we have a set of syntactically unequal,
+but semantically equal types, we can't pick any of them as a representative.
+
+Example:
+
+```
+class Inv<T>
+fun <T> foo(a: Inv<T>, b: Inv<T>): T
+
+fun test(a: Inv<Foo>, b: Inv<Foo!>) {
+    foo(a, b)
+}
+```
+
+In this case, the constraints on `T` are:
+ - `T = Foo`
+ - `T = Foo!`
+
+We have to choose a representative from the set `{ Foo, Foo! }`, and make it the resulting value for type variable `T`.
+Intuitively, `Foo!` is better than `Foo` in this case, but there can be trickier cases as well:
+- `{ List<Foo!>, List<Foo>! }`
+- `{ Foo<Bar!, Bar>, Foo<Bar, Bar!>! }`
+
+The latter case suggests that we need to find a *common dominating type* for a set of types, which is a non-trivial operation.
+
+Let's say that `B` is dominated by `A` and write `B <~ A`, iff
+
+- `A ~~ B`
+- at least one of the following holds
+  - `A == B`
+  - `A = (Al..Au)`, `B = (Bl..Bu)` where `Bl <~ Al`, `Bu <~ Au`
+  - `A == B!`
+  - `A = C<Pa>` or `A = C<Pa>!`, `B = C<Pb>` and `Pb <~ Pa` (for many arguments, analogously)
+  - `A = (Sub<Psub>..Super<Psub>)`, `B = Middle<Pmid>` and
+
+
 
 ## Loading Java Types