diff --git a/codeCore/src/prog8/code/core/Operators.kt b/codeCore/src/prog8/code/core/Operators.kt
index a706e5045..ca4e40abb 100644
--- a/codeCore/src/prog8/code/core/Operators.kt
+++ b/codeCore/src/prog8/code/core/Operators.kt
@@ -3,7 +3,7 @@ package prog8.code.core
 val AssociativeOperators = setOf("+", "*", "&", "|", "^", "or", "and", "xor", "==", "!=")
 val ComparisonOperators = setOf("==", "!=", "<", ">", "<=", ">=")
 val AugmentAssignmentOperators = setOf("+", "-", "/", "*", "&", "|", "^", "<<", ">>", "%", "and", "or", "xor")
-val LogicalOperators = setOf("and", "or", "xor")        // not x is replaced with x==0
+val LogicalOperators = setOf("and", "or", "xor", "not")
 val BitwiseOperators = setOf("&", "|", "^")
 
 fun invertedComparisonOperator(operator: String) =
diff --git a/codeOptimizers/src/prog8/optimizer/ConstantFoldingOptimizer.kt b/codeOptimizers/src/prog8/optimizer/ConstantFoldingOptimizer.kt
index b72d03401..3b3d9c561 100644
--- a/codeOptimizers/src/prog8/optimizer/ConstantFoldingOptimizer.kt
+++ b/codeOptimizers/src/prog8/optimizer/ConstantFoldingOptimizer.kt
@@ -2,7 +2,6 @@ package prog8.optimizer
 
 import prog8.ast.Node
 import prog8.ast.Program
-import prog8.ast.base.ExpressionError
 import prog8.ast.base.FatalAstException
 import prog8.ast.base.UndefinedSymbolError
 import prog8.ast.expressions.*
@@ -14,7 +13,6 @@ import prog8.ast.walk.AstWalker
 import prog8.ast.walk.IAstModification
 import prog8.code.core.AssociativeOperators
 import prog8.code.core.DataType
-import prog8.code.core.IntegerDatatypes
 
 
 class ConstantFoldingOptimizer(private val program: Program) : AstWalker() {
@@ -36,54 +34,8 @@ class ConstantFoldingOptimizer(private val program: Program) : AstWalker() {
     }
 
     override fun after(expr: PrefixExpression, parent: Node): Iterable<IAstModification> {
-        // Try to turn a unary prefix expression into a single constant value.
-        // Compile-time constant sub expressions will be evaluated on the spot.
-        // For instance, the expression for "- 4.5" will be optimized into the float literal -4.5
-        val subexpr = expr.expression
-        if (subexpr is NumericLiteral) {
-            // accept prefixed literal values (such as -3, not true)
-            return when (expr.operator) {
-                "+" -> listOf(IAstModification.ReplaceNode(expr, subexpr, parent))
-                "-" -> when (subexpr.type) {
-                    in IntegerDatatypes -> {
-                        listOf(IAstModification.ReplaceNode(expr,
-                                NumericLiteral.optimalInteger(-subexpr.number.toInt(), subexpr.position),
-                                parent))
-                    }
-                    DataType.FLOAT -> {
-                        listOf(IAstModification.ReplaceNode(expr,
-                                NumericLiteral(DataType.FLOAT, -subexpr.number, subexpr.position),
-                                parent))
-                    }
-                    else -> throw ExpressionError("can only take negative of int or float", subexpr.position)
-                }
-                "~" -> when (subexpr.type) {
-                    DataType.BYTE -> {
-                        listOf(IAstModification.ReplaceNode(expr,
-                                NumericLiteral(DataType.BYTE, subexpr.number.toInt().inv().toDouble(), subexpr.position),
-                                parent))
-                    }
-                    DataType.UBYTE -> {
-                        listOf(IAstModification.ReplaceNode(expr,
-                                NumericLiteral(DataType.UBYTE, (subexpr.number.toInt().inv() and 255).toDouble(), subexpr.position),
-                                parent))
-                    }
-                    DataType.WORD -> {
-                        listOf(IAstModification.ReplaceNode(expr,
-                                NumericLiteral(DataType.WORD, subexpr.number.toInt().inv().toDouble(), subexpr.position),
-                                parent))
-                    }
-                    DataType.UWORD -> {
-                        listOf(IAstModification.ReplaceNode(expr,
-                                NumericLiteral(DataType.UWORD, (subexpr.number.toInt().inv() and 65535).toDouble(), subexpr.position),
-                                parent))
-                    }
-                    else -> throw ExpressionError("can only take bitwise inversion of int", subexpr.position)
-                }
-                else -> throw ExpressionError(expr.operator, subexpr.position)
-            }
-        }
-        return noModifications
+        val constValue = expr.constValue(program) ?: return noModifications
+        return listOf(IAstModification.ReplaceNode(expr, constValue, parent))
     }
 
     /*
diff --git a/compiler/src/prog8/compiler/Compiler.kt b/compiler/src/prog8/compiler/Compiler.kt
index 44b1deebe..dcdb86e0d 100644
--- a/compiler/src/prog8/compiler/Compiler.kt
+++ b/compiler/src/prog8/compiler/Compiler.kt
@@ -330,6 +330,8 @@ private fun processAst(program: Program, errors: IErrorReporter, compilerOptions
     errors.report()
     program.reorderStatements(errors, compilerOptions)
     errors.report()
+    program.changeNotExpression(errors)
+    errors.report()
     program.addTypecasts(errors, compilerOptions)
     errors.report()
     program.variousCleanups(errors, compilerOptions)
diff --git a/compiler/src/prog8/compiler/astprocessing/AstExtensions.kt b/compiler/src/prog8/compiler/astprocessing/AstExtensions.kt
index 0d8c14398..6480b12fb 100644
--- a/compiler/src/prog8/compiler/astprocessing/AstExtensions.kt
+++ b/compiler/src/prog8/compiler/astprocessing/AstExtensions.kt
@@ -44,6 +44,14 @@ internal fun Program.reorderStatements(errors: IErrorReporter, options: Compilat
     }
 }
 
+internal fun Program.changeNotExpression(errors: IErrorReporter) {
+    val changer = NotExpressionChanger(this, errors)
+    changer.visit(this)
+    while(errors.noErrors() && changer.applyModifications()>0) {
+        changer.visit(this)
+    }
+}
+
 internal fun Program.charLiteralsToUByteLiterals(target: ICompilationTarget, errors: IErrorReporter) {
     val walker = object : AstWalker() {
         override fun after(char: CharLiteral, parent: Node): Iterable<IAstModification> {
diff --git a/compiler/src/prog8/compiler/astprocessing/AstPreprocessor.kt b/compiler/src/prog8/compiler/astprocessing/AstPreprocessor.kt
index f1c008a45..7282efd61 100644
--- a/compiler/src/prog8/compiler/astprocessing/AstPreprocessor.kt
+++ b/compiler/src/prog8/compiler/astprocessing/AstPreprocessor.kt
@@ -3,7 +3,6 @@ package prog8.compiler.astprocessing
 import prog8.ast.IFunctionCall
 import prog8.ast.Node
 import prog8.ast.Program
-import prog8.ast.base.FatalAstException
 import prog8.ast.base.SyntaxError
 import prog8.ast.expressions.*
 import prog8.ast.statements.*
@@ -114,17 +113,6 @@ class AstPreprocessor(val program: Program, val errors: IErrorReporter, val comp
         return noModifications
     }
 
-    override fun before(expr: PrefixExpression, parent: Node): Iterable<IAstModification> {
-        if(expr.operator == "not") {
-            // not(x)  -->  x==0
-            // this means that "not" will never occur anywhere again in the ast
-            val dt = expr.expression.inferType(program).getOr(DataType.UBYTE)
-            val replacement = BinaryExpression(expr.expression, "==", NumericLiteral(dt,0.0, expr.position), expr.position)
-            return listOf(IAstModification.ReplaceNodeSafe(expr, replacement, parent))
-        }
-        return noModifications
-    }
-
     override fun after(decl: VarDecl, parent: Node): Iterable<IAstModification> {
         val nextAssignment = decl.nextSibling() as? Assignment
         if(nextAssignment!=null && nextAssignment.origin!=AssignmentOrigin.VARINIT) {
@@ -164,6 +152,8 @@ class AstPreprocessor(val program: Program, val errors: IErrorReporter, val comp
             expr
         else if(expr is BinaryExpression && expr.operator in LogicalOperators+ComparisonOperators)
             expr
+        else if(expr is PrefixExpression && expr.operator in LogicalOperators)
+            expr
         else
             FunctionCallExpression(IdentifierReference(listOf("boolean"), expr.position), mutableListOf(expr), expr.position)
     }
diff --git a/compiler/src/prog8/compiler/astprocessing/BeforeAsmAstChanger.kt b/compiler/src/prog8/compiler/astprocessing/BeforeAsmAstChanger.kt
index fba3c293f..3fc37769d 100644
--- a/compiler/src/prog8/compiler/astprocessing/BeforeAsmAstChanger.kt
+++ b/compiler/src/prog8/compiler/astprocessing/BeforeAsmAstChanger.kt
@@ -231,8 +231,12 @@ internal class BeforeAsmAstChanger(val program: Program,
         var rightAssignment: Assignment? = null
         var rightOperandReplacement: Expression? = null
 
-        val separateLeftExpr = !expr.left.isSimple && expr.left !is IFunctionCall && expr.left !is ContainmentCheck
-        val separateRightExpr = !expr.right.isSimple && expr.right !is IFunctionCall && expr.right !is ContainmentCheck
+        val separateLeftExpr = !expr.left.isSimple
+                && expr.left !is IFunctionCall
+                && expr.left !is ContainmentCheck
+        val separateRightExpr = !expr.right.isSimple
+                && expr.right !is IFunctionCall
+                && expr.right !is ContainmentCheck
         val leftDt = expr.left.inferType(program)
         val rightDt = expr.right.inferType(program)
 
diff --git a/compiler/src/prog8/compiler/astprocessing/CodeDesugarer.kt b/compiler/src/prog8/compiler/astprocessing/CodeDesugarer.kt
index 3796f8b77..eac6ac9b3 100644
--- a/compiler/src/prog8/compiler/astprocessing/CodeDesugarer.kt
+++ b/compiler/src/prog8/compiler/astprocessing/CodeDesugarer.kt
@@ -1,7 +1,10 @@
 package prog8.compiler.astprocessing
 
 import prog8.ast.*
-import prog8.ast.expressions.*
+import prog8.ast.expressions.BinaryExpression
+import prog8.ast.expressions.DirectMemoryRead
+import prog8.ast.expressions.FunctionCallExpression
+import prog8.ast.expressions.NumericLiteral
 import prog8.ast.statements.*
 import prog8.ast.walk.AstWalker
 import prog8.ast.walk.IAstModification
diff --git a/compiler/src/prog8/compiler/astprocessing/NotExpressionChanger.kt b/compiler/src/prog8/compiler/astprocessing/NotExpressionChanger.kt
new file mode 100644
index 000000000..7e2f432b8
--- /dev/null
+++ b/compiler/src/prog8/compiler/astprocessing/NotExpressionChanger.kt
@@ -0,0 +1,113 @@
+package prog8.compiler.astprocessing
+
+import prog8.ast.Node
+import prog8.ast.Program
+import prog8.ast.expressions.BinaryExpression
+import prog8.ast.expressions.Expression
+import prog8.ast.expressions.NumericLiteral
+import prog8.ast.expressions.PrefixExpression
+import prog8.ast.statements.Assignment
+import prog8.ast.walk.AstWalker
+import prog8.ast.walk.IAstModification
+import prog8.code.core.IErrorReporter
+import prog8.code.core.IntegerDatatypes
+
+internal class NotExpressionChanger(val program: Program, val errors: IErrorReporter) : AstWalker() {
+
+    override fun before(expr: BinaryExpression, parent: Node): Iterable<IAstModification> {
+        if(expr.operator=="==" || expr.operator=="!=") {
+            val left = expr.left as? BinaryExpression
+            if (left != null) {
+                val rightValue = expr.right.constValue(program)
+                if (rightValue?.number == 0.0 && rightValue.type in IntegerDatatypes) {
+                    if (left.operator == "==" && expr.operator == "==") {
+                        // (x==something)==0  -->  x!=something
+                        left.operator = "!="
+                        return listOf(IAstModification.ReplaceNode(expr, left, parent))
+                    } else if (left.operator == "!=" && expr.operator == "==") {
+                        // (x!=something)==0  -->  x==something
+                        left.operator = "=="
+                        return listOf(IAstModification.ReplaceNode(expr, left, parent))
+                    } else if (left.operator == "==" && expr.operator == "!=") {
+                        // (x==something)!=0 --> x==something
+                        left.operator = "=="
+                        return listOf(IAstModification.ReplaceNode(expr, left, parent))
+                    } else if (left.operator == "!=" && expr.operator == "!=") {
+                        // (x!=something)!=0 --> x!=something
+                        left.operator = "!="
+                        return listOf(IAstModification.ReplaceNode(expr, left, parent))
+                    }
+                }
+            }
+        }
+
+        val left = expr.left as? BinaryExpression
+        val right = expr.right as? BinaryExpression
+        val leftValue = left?.right?.constValue(program)?.number
+        val rightValue = right?.right?.constValue(program)?.number
+
+        if(expr.operator == "or") {
+            if(left?.operator=="==" && right?.operator=="==" && leftValue==0.0 && rightValue==0.0) {
+                // (a==0) or (b==0) -> (a and b)==0
+                val orExpr = BinaryExpression(left.left, "and", right.left, expr.position)
+                val equalsZero = BinaryExpression(orExpr, "==", NumericLiteral.fromBoolean(false, expr.position), expr.position)
+                return listOf(IAstModification.ReplaceNode(expr, equalsZero, parent))
+            }
+        }
+        else if(expr.operator == "and") {
+            if(left?.operator=="==" && right?.operator=="==" && leftValue==0.0 && rightValue==0.0) {
+                // (a==0) and (b==0) -> (a or b)==0
+                val orExpr = BinaryExpression(left.left, "or", right.left, expr.position)
+                val equalsZero = BinaryExpression(orExpr, "==", NumericLiteral.fromBoolean(false, expr.position), expr.position)
+                return listOf(IAstModification.ReplaceNode(expr, equalsZero, parent))
+            }
+        }
+        return noModifications
+    }
+
+    override fun after(expr: BinaryExpression, parent: Node): Iterable<IAstModification> {
+        // not a or not b  -> not(a and b)
+        if(expr.operator=="or") {
+            val left = expr.left as? PrefixExpression
+            val right = expr.right as? PrefixExpression
+            if(left?.operator=="not" && right?.operator=="not") {
+                val andExpr = BinaryExpression(left.expression, "and", right.expression, expr.position)
+                val notExpr = PrefixExpression("not", andExpr, expr.position)
+                return listOf(IAstModification.ReplaceNode(expr, notExpr, parent))
+            }
+        }
+
+        // not a and not b -> not(a or b)
+        if(expr.operator=="and") {
+            val left = expr.left as? PrefixExpression
+            val right = expr.right as? PrefixExpression
+            if(left?.operator=="not" && right?.operator=="not") {
+                val andExpr = BinaryExpression(left.expression, "or", right.expression, expr.position)
+                val notExpr = PrefixExpression("not", andExpr, expr.position)
+                return listOf(IAstModification.ReplaceNode(expr, notExpr, parent))
+            }
+        }
+
+        if(expr.operator=="==") {
+            val rightValue = expr.right.constValue(program)
+            if(rightValue?.number==0.0 && rightValue.type in IntegerDatatypes) {
+                // x==0 -> not x (only if occurs as a subexpression)
+                if(expr.parent is Expression || expr.parent is Assignment) {
+                    val notExpr = PrefixExpression("not", expr.left.copy(), expr.position)
+                    return listOf(IAstModification.ReplaceNodeSafe(expr, notExpr, parent))
+                }
+            }
+        }
+
+        return noModifications
+    }
+
+    override fun after(expr: PrefixExpression, parent: Node): Iterable<IAstModification> {
+        if(expr.operator == "not") {
+            // not(not(x)) -> x
+            if((expr.expression as? PrefixExpression)?.operator=="not")
+                return listOf(IAstModification.ReplaceNode(expr, expr.expression, parent))
+        }
+        return noModifications
+    }
+}
diff --git a/compiler/src/prog8/compiler/astprocessing/StatementReorderer.kt b/compiler/src/prog8/compiler/astprocessing/StatementReorderer.kt
index 1d02eeb66..a8e2fc77d 100644
--- a/compiler/src/prog8/compiler/astprocessing/StatementReorderer.kt
+++ b/compiler/src/prog8/compiler/astprocessing/StatementReorderer.kt
@@ -306,12 +306,14 @@ internal class StatementReorderer(val program: Program,
                         val newRight = BinaryExpression(leftBinExpr.right, binExpr.operator, binExpr.right, binExpr.position)
                         val newValue = BinaryExpression(leftBinExpr.left, binExpr.operator, newRight, binExpr.position)
                         listOf(IAstModification.ReplaceNode(binExpr, newValue, assignment))
-                    } else {
+                    }
+                    else if(leftBinExpr.left.constValue(program)!=null && binExpr.right.constValue(program)!=null) {
                         // A = (x <associative-operator> A) <same-operator> y ==> A = A <associative-operator> (x <same-operator> y)
                         val newRight = BinaryExpression(leftBinExpr.left, binExpr.operator, binExpr.right, binExpr.position)
                         val newValue = BinaryExpression(leftBinExpr.right, binExpr.operator, newRight, binExpr.position)
                         listOf(IAstModification.ReplaceNode(binExpr, newValue, assignment))
                     }
+                    else noModifications
                 }
                 val rightBinExpr = binExpr.right as? BinaryExpression
                 if(rightBinExpr?.operator == binExpr.operator) {
diff --git a/compiler/src/prog8/compiler/astprocessing/VariousCleanups.kt b/compiler/src/prog8/compiler/astprocessing/VariousCleanups.kt
index f4eca15ac..2eb321c5f 100644
--- a/compiler/src/prog8/compiler/astprocessing/VariousCleanups.kt
+++ b/compiler/src/prog8/compiler/astprocessing/VariousCleanups.kt
@@ -48,7 +48,7 @@ internal class VariousCleanups(val program: Program, val errors: IErrorReporter,
         if(parent is Assignment) {
             val targetDt = (parent).target.inferType(program).getOrElse { throw FatalAstException("invalid dt") }
             if(sourceDt istype targetDt) {
-                // we can get rid of this typecast because the type is already
+                // we can get rid of this typecast because the type is already the target type
                 return listOf(IAstModification.ReplaceNode(typecast, typecast.expression, parent))
             }
         }
@@ -71,6 +71,13 @@ internal class VariousCleanups(val program: Program, val errors: IErrorReporter,
             // +X --> X
             return listOf(IAstModification.ReplaceNode(expr, expr.expression, parent))
         }
+        else if(expr.operator == "not") {
+            // not(x)  -->  x==0
+            // this means that "not" will never occur anywhere again in the ast after this
+            val dt = expr.expression.inferType(program).getOr(DataType.UBYTE)
+            val replacement = BinaryExpression(expr.expression, "==", NumericLiteral(dt,0.0, expr.position), expr.position)
+            return listOf(IAstModification.ReplaceNodeSafe(expr, replacement, parent))
+        }
         return noModifications
     }
 
diff --git a/compiler/test/TestOptimization.kt b/compiler/test/TestOptimization.kt
index 19d173126..d4165a6e3 100644
--- a/compiler/test/TestOptimization.kt
+++ b/compiler/test/TestOptimization.kt
@@ -1,12 +1,10 @@
 package prog8tests
 
-import io.kotest.assertions.fail
 import io.kotest.assertions.withClue
 import io.kotest.core.spec.style.FunSpec
 import io.kotest.matchers.shouldBe
 import io.kotest.matchers.shouldNotBe
 import io.kotest.matchers.string.shouldContain
-import io.kotest.matchers.string.shouldNotBeBlank
 import io.kotest.matchers.string.shouldStartWith
 import io.kotest.matchers.types.instanceOf
 import io.kotest.matchers.types.shouldBeSameInstanceAs
@@ -14,9 +12,9 @@ import prog8.ast.ParentSentinel
 import prog8.ast.Program
 import prog8.ast.expressions.*
 import prog8.ast.statements.*
-import prog8.code.core.*
+import prog8.code.core.DataType
+import prog8.code.core.Position
 import prog8.code.target.C64Target
-import prog8.compiler.astprocessing.processAstBeforeAsmGeneration
 import prog8.compiler.printProgram
 import prog8tests.helpers.*
 
@@ -253,83 +251,41 @@ class TestOptimization: FunSpec({
         (initY2.value as NumericLiteral).number shouldBe 11.0
     }
 
-    test("not-typecasted assignment from ubyte logical expression to uword var should be auto upcasted") {
+    test("various 'not' operator rewrites even without optimizations on") {
         val src = """
             main {
                 sub start() {
-                    ubyte bb
-                    uword ww
-                    ww = not bb or not ww       ; expression combining ubyte and uword
+                    ubyte a1
+                    ubyte a2
+                    a1 = not not a1             ; a1 = a1==0
+                    a1 = not a1 or not a2       ; a1 = (a1 and a2)==0
+                    a1 = not a1 and not a2      ; a1 = (a1 or a2)==0
                 }
             }
         """
         val result = compileText(C64Target(), false, src, writeAssembly = false)!!
+        val stmts = result.program.entrypoint.statements
+        stmts.size shouldBe 7
 
-        val wwAssign = result.program.entrypoint.statements.last() as Assignment
-        val expr = wwAssign.value as TypecastExpression
-        expr.type shouldBe DataType.UWORD
-
-        wwAssign.target.identifier?.nameInSource shouldBe listOf("ww")
-        expr.expression.inferType(result.program) istype DataType.UBYTE shouldBe true
-    }
-
-    test("intermediate assignment steps have correct types for codegen phase (BeforeAsmGenerationAstChanger)") {
-        val src = """
-            main {
-                sub start() {
-                    ubyte bb
-                    uword ww
-                    bb = not bb or not ww       ; expression combining ubyte and uword
-                }
-            }
-        """
-        val result = compileText(C64Target(), false, src, writeAssembly = false)!!
-
-        // bb = ((boolean(bb)==0) or (boolean(ww)==0))
-        val bbAssign = result.program.entrypoint.statements.last() as Assignment
-        val expr = bbAssign.value as BinaryExpression
-        expr.operator shouldBe "or"
-        expr.left shouldBe instanceOf<BinaryExpression>()
-        expr.right shouldBe instanceOf<BinaryExpression>()
-        expr.left.inferType(result.program).getOrElse { fail("dt") } shouldBe DataType.UBYTE
-        expr.right.inferType(result.program).getOrElse { fail("dt") } shouldBe DataType.UBYTE
-        expr.inferType(result.program).getOrElse { fail("dt") } shouldBe DataType.UBYTE
-
-        val options = CompilationOptions(OutputType.PRG, CbmPrgLauncherType.BASIC, ZeropageType.DONTUSE, emptyList(),
-            floats = false,
-            noSysInit = true,
-            compTarget = C64Target(),
-            loadAddress = 0u, outputDir= outputDir)
-        result.program.processAstBeforeAsmGeneration(options, ErrorReporterForTests())
-        printProgram(result.program)
-
-        // TODO this is no longer the case:
-        // assignment is now split into:
-        //     bb =  not bb
-        //     bb = (bb or  (not ww as ubyte)
-//        val assigns = result.program.entrypoint.statements.filterIsInstance<Assignment>()
-//        val bbAssigns = assigns.filter { it.value !is NumericLiteral }
-//        bbAssigns.size shouldBe 2
-//
-//        bbAssigns[0].target.identifier!!.nameInSource shouldBe listOf("bb")
-//        bbAssigns[0].value shouldBe instanceOf<PrefixExpression>()
-//        (bbAssigns[0].value as PrefixExpression).operator shouldBe "not"
-//        ((bbAssigns[0].value as PrefixExpression).expression as? IdentifierReference)?.nameInSource shouldBe listOf("bb")
-//        bbAssigns[0].value.inferType(result.program).getOrElse { fail("dt") } shouldBe DataType.UBYTE
-//
-//        bbAssigns[1].target.identifier!!.nameInSource shouldBe listOf("bb")
-//        val bbAssigns1expr = bbAssigns[1].value as BinaryExpression
-//        bbAssigns1expr.operator shouldBe "or"
-//        (bbAssigns1expr.left as? IdentifierReference)?.nameInSource shouldBe listOf("bb")
-//        bbAssigns1expr.right shouldBe instanceOf<TypecastExpression>()
-//        val castedValue = (bbAssigns1expr.right as TypecastExpression).expression as PrefixExpression
-//        castedValue.operator shouldBe "not"
-//        (castedValue.expression as? IdentifierReference)?.nameInSource shouldBe listOf("ww")
-//        bbAssigns1expr.inferType(result.program).getOrElse { fail("dt") } shouldBe DataType.UBYTE
-//
-//        val asm = generateAssembly(result.program, options)
-//        asm shouldNotBe null
-//        asm!!.name.shouldNotBeBlank()
+        val value1 = (stmts[4] as Assignment).value as BinaryExpression
+        val value2 = (stmts[5] as Assignment).value as BinaryExpression
+        val value3 = (stmts[6] as Assignment).value as BinaryExpression
+        value1.operator shouldBe "=="
+        value1.right shouldBe NumericLiteral(DataType.UBYTE, 0.0, Position.DUMMY)
+        value2.operator shouldBe "=="
+        value2.right shouldBe NumericLiteral(DataType.UBYTE, 0.0, Position.DUMMY)
+        value3.operator shouldBe "=="
+        value3.right shouldBe NumericLiteral(DataType.UBYTE, 0.0, Position.DUMMY)
+        val left1 = value1.left as IdentifierReference
+        val left2 = value2.left as BinaryExpression
+        val left3 = value3.left as BinaryExpression
+        left1.nameInSource shouldBe listOf("a1")
+        left2.operator shouldBe "and"
+        (left2.left as IdentifierReference).nameInSource shouldBe listOf("a1")
+        (left2.right as IdentifierReference).nameInSource shouldBe listOf("a2")
+        left3.operator shouldBe "or"
+        (left3.left as IdentifierReference).nameInSource shouldBe listOf("a1")
+        (left3.right as IdentifierReference).nameInSource shouldBe listOf("a2")
     }
 
     test("intermediate assignment steps generated for typecasted expression") {
diff --git a/compiler/test/TestTypecasts.kt b/compiler/test/TestTypecasts.kt
index 15082c133..b841bf9a3 100644
--- a/compiler/test/TestTypecasts.kt
+++ b/compiler/test/TestTypecasts.kt
@@ -180,7 +180,7 @@ class TestTypecasts: FunSpec({
             }"""
         val result = compileText(C64Target(), false, text, writeAssembly = true)!!
         val statements = result.program.entrypoint.statements
-        statements.size shouldBe 13
+        statements.size shouldBe 14
     }
 
     test("no infinite typecast loop in assignment asmgen") {
diff --git a/compilerAst/src/prog8/ast/expressions/AstExpressions.kt b/compilerAst/src/prog8/ast/expressions/AstExpressions.kt
index c64e8d8d7..a7ef7a44d 100644
--- a/compilerAst/src/prog8/ast/expressions/AstExpressions.kt
+++ b/compilerAst/src/prog8/ast/expressions/AstExpressions.kt
@@ -109,6 +109,7 @@ class PrefixExpression(val operator: String, var expression: Expression, overrid
                 DataType.UWORD -> NumericLiteral(DataType.UWORD, (constval.number.toInt().inv() and 65535).toDouble(), constval.position)
                 else -> throw ExpressionError("can only take bitwise inversion of int", constval.position)
             }
+            "not" -> NumericLiteral.fromBoolean(constval.number==0.0, constval.position)
             else -> throw FatalAstException("invalid operator")
         }
         converted.linkParents(this.parent)
@@ -214,7 +215,7 @@ class BinaryExpression(var left: Expression, var operator: String, var right: Ex
             "&" -> leftDt
             "|" -> leftDt
             "^" -> leftDt
-            "and", "or", "xor" -> InferredTypes.knownFor(DataType.UBYTE)
+            "and", "or", "xor", "not" -> InferredTypes.knownFor(DataType.UBYTE)
             "<", ">",
             "<=", ">=",
             "==", "!=" -> dynamicBooleanType()
diff --git a/docs/source/todo.rst b/docs/source/todo.rst
index 74e9ab406..f382859b2 100644
--- a/docs/source/todo.rst
+++ b/docs/source/todo.rst
@@ -3,33 +3,32 @@ TODO
 
 For next release
 ^^^^^^^^^^^^^^^^
-- code gen for if statements has become bad
+- assembler incorrectly assembles hello.asm now (crash when run)
+
+- why can't while and until loops use NOT condition instead of Cond==0 ? Fix this!
+
+- code gen for if statements has become inefficient? vm/6502?
         if not diskio.iteration_in_progress or not num_bytes
             return 0
-- code gen for while loops has become bad  (until loops probably as well)
+- code gen for while loops has become inefficient:  (until loops probably as well)
   (maybe solved when if statements code has been fixed)
              while c64.CHRIN()!='\"'  {
                 if c64.READST()
                     goto close_end
             }
 
-- chess.prg became A LOT larger, why!?  (perhaps due to new while/until condition handling?)
-- imageviewer.prg became A LOT larger, why!?
-- petaxian.prg became A LOT larger, why!?
-- some programs became a bit larger since "not" was removed (assembler)
-
-- 6502: fix logical and/or/xor routines to just be bitwise routines.
+- petaxian.prg became quite a bit (200 bytes) larger, why!? because of the above?
 
 - get rid of logical and/or/xor in the codegen (6502+vm)
   because bitwise versions + correct use of boolean() operand wrapping are equivalent?
-  can do this for instance by replacing and/or/xor with their bitwise versions &, |, ^, ~
+  can do this for instance by replacing and/or/xor with their bitwise versions &, |, ^
+- ...or: 6502: fix logical and/or/xor routines to just be bitwise routines.
+
+- check all examples if they still work, maybe we find bug for...:
 
 - compiling logical.p8 to virtual with optimization generates a lot larger code as without optimizations.
   this is not the case for the 6502 codegen.
 
-- add optimizations: not a or not b  -> not(a and b)      ,  not a and not b -> not(a or b)
-  actually this now means: (a==0) or (b==0) -> (a or b)==0,  (a==0) and (b==0) -> (a or b)==0
-  add unit tests for that.
 - bin expr splitter: split logical expressions on ands/ors/xors ?
 
 - add some more optimizations in vmPeepholeOptimizer
diff --git a/examples/test.p8 b/examples/test.p8
index ffa725849..e94619f2d 100644
--- a/examples/test.p8
+++ b/examples/test.p8
@@ -6,22 +6,56 @@
 main  {
 
     sub start() {
-        ; a "pixelshader":
-        sys.gfx_enable(0)       ; enable lo res screen
-        ubyte shifter
+        ubyte a1 = 0
+        ubyte a2 = 42
+        ubyte a3 = 1
 
-        repeat {
-            uword xx
-            uword yy = 0
-            repeat 240 {
-                xx = 0
-                repeat 320 {
-                    sys.gfx_plot(xx, yy, xx*yy + shifter as ubyte)
-                    xx++
-                }
-                yy++
-            }
-            shifter+=4
-        }
-    }
+        if (a1==0)==0
+            a3 = (a1==0)==0
+
+        if (a1!=0)==0
+            a3 = (a1!=0)==0
+
+        if (a1==0)!=0
+            a3 = (a1==0)!=0
+
+        if (a1!=0)!=0
+            a3 = (a1!=0)!=0
+
+        if (a1==0) or (a2==0)
+            a3 = (a1==0) or (a2==0)
+
+        if (a1==0) and (a2==0)
+            a3 = (a1==0) and (a2==0)
+
+        if not a1 or not a2 or not(not(a3))
+            a3=not a1 or not a2 or not(not(a3))
+
+        if (a1==0) or (a2==0)
+            a3 = (a1==0) or (a2==0)
+
+        if (a1==0) and (a2==0)
+            a3 = (a1==0) and (a2==0)
+
+        txt.print_ub(a3)
+
+
+;        ; a "pixelshader":
+;        sys.gfx_enable(0)       ; enable lo res screen
+;        ubyte shifter
+;
+;        repeat {
+;            uword xx
+;            uword yy = 0
+;            repeat 240 {
+;                xx = 0
+;                repeat 320 {
+;                    sys.gfx_plot(xx, yy, xx*yy + shifter as ubyte)
+;                    xx++
+;                }
+;                yy++
+;            }
+;            shifter+=4
+;        }
+     }
 }