diff --git a/Triangle.AbstractMachine.Disassembler/build.gradle b/Triangle.AbstractMachine.Disassembler/build.gradle
index 075e008..90e01e7 100644
--- a/Triangle.AbstractMachine.Disassembler/build.gradle
+++ b/Triangle.AbstractMachine.Disassembler/build.gradle
@@ -1,7 +1,7 @@
 apply plugin: 'java'
 apply plugin: 'application'
 
-sourceCompatibility = 17
+sourceCompatibility = 11
 
 dependencies {
 	implementation project(':Triangle.AbstractMachine')
diff --git a/Triangle.AbstractMachine.Interpreter/build.gradle b/Triangle.AbstractMachine.Interpreter/build.gradle
index cf4fad0..38c7835 100644
--- a/Triangle.AbstractMachine.Interpreter/build.gradle
+++ b/Triangle.AbstractMachine.Interpreter/build.gradle
@@ -1,7 +1,7 @@
 apply plugin: 'java'
 apply plugin: 'application'
 
-sourceCompatibility = 17
+sourceCompatibility = 11
 
 dependencies {
 	implementation project(':Triangle.AbstractMachine')
diff --git a/Triangle.AbstractMachine/build.gradle b/Triangle.AbstractMachine/build.gradle
index 4324881..80f98eb 100644
--- a/Triangle.AbstractMachine/build.gradle
+++ b/Triangle.AbstractMachine/build.gradle
@@ -1,4 +1,4 @@
 apply plugin: 'java-library'
 apply plugin: 'eclipse'
 
-sourceCompatibility = 17
\ No newline at end of file
+sourceCompatibility = 11
\ No newline at end of file
diff --git a/Triangle.Compiler/build.gradle b/Triangle.Compiler/build.gradle
index 326eb52..a27ea3f 100644
--- a/Triangle.Compiler/build.gradle
+++ b/Triangle.Compiler/build.gradle
@@ -1,7 +1,7 @@
 apply plugin: 'java'
 apply plugin: 'application'
 
-sourceCompatibility = 17
+sourceCompatibility = 11
 
 dependencies {
 	implementation project(':Triangle.AbstractMachine')
diff --git a/Triangle.Compiler/src/main/java/triangle/abstractSyntaxTrees/formals/ConstFormalParameter.java b/Triangle.Compiler/src/main/java/triangle/abstractSyntaxTrees/formals/ConstFormalParameter.java
index 9bd646c..c860a53 100644
--- a/Triangle.Compiler/src/main/java/triangle/abstractSyntaxTrees/formals/ConstFormalParameter.java
+++ b/Triangle.Compiler/src/main/java/triangle/abstractSyntaxTrees/formals/ConstFormalParameter.java
@@ -39,8 +39,8 @@ public class ConstFormalParameter extends FormalParameter implements ConstantDec
 
 	@Override
 	public boolean equals(Object fpAST) {
-		if (fpAST instanceof ConstFormalParameter cfpAST) {
-			return T.equals(cfpAST.T);
+		if (fpAST instanceof ConstFormalParameter) {
+			return T.equals(((ConstFormalParameter)fpAST).T);
 		} else {
 			return false;
 		}
diff --git a/Triangle.Compiler/src/main/java/triangle/abstractSyntaxTrees/formals/VarFormalParameter.java b/Triangle.Compiler/src/main/java/triangle/abstractSyntaxTrees/formals/VarFormalParameter.java
index 57cfdbc..19efd56 100644
--- a/Triangle.Compiler/src/main/java/triangle/abstractSyntaxTrees/formals/VarFormalParameter.java
+++ b/Triangle.Compiler/src/main/java/triangle/abstractSyntaxTrees/formals/VarFormalParameter.java
@@ -39,8 +39,8 @@ public class VarFormalParameter extends FormalParameter implements VariableDecla
 
 	@Override
 	public boolean equals(Object fpAST) {
-		if (fpAST instanceof VarFormalParameter vfpAST) {
-			return T.equals(vfpAST.T);
+		if (fpAST instanceof VarFormalParameter) {
+			return T.equals(((VarFormalParameter)fpAST).T);
 		} else {
 			return false;
 		}
diff --git a/Triangle.Compiler/src/main/java/triangle/contextualAnalyzer/Checker.java b/Triangle.Compiler/src/main/java/triangle/contextualAnalyzer/Checker.java
index 9a9f5b2..56a3a2e 100644
--- a/Triangle.Compiler/src/main/java/triangle/contextualAnalyzer/Checker.java
+++ b/Triangle.Compiler/src/main/java/triangle/contextualAnalyzer/Checker.java
@@ -132,7 +132,8 @@ public final class Checker implements ActualParameterVisitor<FormalParameter, Vo
 	public Void visitCallCommand(CallCommand ast, Void arg) {
 		var binding = ast.I.visit(this);
 
-		if (binding instanceof ProcedureDeclaration procedure) {
+		if (binding instanceof ProcedureDeclaration) {
+			ProcedureDeclaration procedure = (ProcedureDeclaration)binding;
 			ast.APS.visit(this, procedure.getFormals());
 		} else {
 			reportUndeclaredOrError(binding, ast.I, "\"%\" is not a procedure identifier");
@@ -203,7 +204,8 @@ public final class Checker implements ActualParameterVisitor<FormalParameter, Vo
 		var e2Type = ast.E2.visit(this);
 		var binding = ast.O.visit(this);
 
-		if (binding instanceof BinaryOperatorDeclaration bbinding) {
+		if (binding instanceof BinaryOperatorDeclaration) {
+			BinaryOperatorDeclaration bbinding = (BinaryOperatorDeclaration)binding;
 			if (bbinding.ARG1.equals(StdEnvironment.anyType)) {
 				// this operator must be "=" or "\="
 				checkAndReportError(e1Type.equals(e2Type), "incompatible argument types for \"%\"", ast.O, ast);
@@ -222,7 +224,8 @@ public final class Checker implements ActualParameterVisitor<FormalParameter, Vo
 	public TypeDenoter visitCallExpression(CallExpression ast, Void arg) {
 		var binding = ast.I.visit(this);
 
-		if (binding instanceof FunctionDeclaration function) {
+		if (binding instanceof FunctionDeclaration) {
+			FunctionDeclaration function = (FunctionDeclaration)binding;
 			ast.APS.visit(this, function.getFormals());
 			return ast.type = function.getType();
 		}
@@ -277,7 +280,8 @@ public final class Checker implements ActualParameterVisitor<FormalParameter, Vo
 		var eType = ast.E.visit(this);
 		var binding = ast.O.visit(this);
 
-		if (binding instanceof UnaryOperatorDeclaration ubinding) {
+		if (binding instanceof UnaryOperatorDeclaration) {
+			UnaryOperatorDeclaration ubinding = (UnaryOperatorDeclaration)binding;
 			checkAndReportError(eType.equals(ubinding.ARG), "wrong argument type for \"%\"", ast.O);
 			return ast.type = ubinding.RES;
 		}
@@ -472,8 +476,9 @@ public final class Checker implements ActualParameterVisitor<FormalParameter, Vo
 	@Override
 	public Void visitConstActualParameter(ConstActualParameter ast, FormalParameter arg) {
 		var eType = ast.E.visit(this);
-		if (arg instanceof ConstFormalParameter param) {
-			checkAndReportError(eType.equals(param.T), "wrong type for const actual parameter", ast.E);
+		if (arg instanceof ConstFormalParameter) {
+			ConstFormalParameter param = (ConstFormalParameter)arg;
+			checkAndReportError(eType.equals(((ConstFormalParameter)arg).T), "wrong type for const actual parameter", ast.E);
 		} else {
 			reportError("const actual parameter not expected here", ast);
 		}
@@ -483,10 +488,12 @@ public final class Checker implements ActualParameterVisitor<FormalParameter, Vo
 	@Override
 	public Void visitFuncActualParameter(FuncActualParameter ast, FormalParameter arg) {
 		var binding = ast.I.visit(this);
-		if (binding instanceof FunctionDeclaration function) {
+		if (binding instanceof FunctionDeclaration) {
+			FunctionDeclaration function = (FunctionDeclaration)binding;
 			var formals = function.getFormals();
 			var functionType = function.getType();
-			if (arg instanceof FuncFormalParameter param) {
+			if (arg instanceof FuncFormalParameter) {
+				FuncFormalParameter param = (FuncFormalParameter)arg;
 				if (!formals.equals(param.getFormals())) {
 					reportError("wrong signature for function \"%\"", ast.I);
 				} else if (!functionType.equals(param.T)) {
@@ -504,9 +511,11 @@ public final class Checker implements ActualParameterVisitor<FormalParameter, Vo
 	@Override
 	public Void visitProcActualParameter(ProcActualParameter ast, FormalParameter arg) {
 		var binding = ast.I.visit(this);
-		if (binding instanceof ProcedureDeclaration procedure) {
+		if (binding instanceof ProcedureDeclaration) {
+			ProcedureDeclaration procedure = (ProcedureDeclaration)binding;
 			var formals = procedure.getFormals();
-			if (arg instanceof ProcFormalParameter param) {
+			if (arg instanceof ProcFormalParameter) {
+				ProcFormalParameter param = (ProcFormalParameter)arg;
 				checkAndReportError(formals.equals(param.getFormals()), "wrong signature for procedure \"%\"", ast.I);
 			} else {
 				reportError("proc actual parameter not expected here", ast);
@@ -522,7 +531,8 @@ public final class Checker implements ActualParameterVisitor<FormalParameter, Vo
 		var vType = ast.V.visit(this);
 		if (!ast.V.variable) {
 			reportError("actual parameter is not a variable", ast.V);
-		} else if (arg instanceof VarFormalParameter parameter) {
+		} else if (arg instanceof VarFormalParameter) {
+			VarFormalParameter parameter = (VarFormalParameter)arg;
 			checkAndReportError(vType.equals(parameter.T), "wrong type for var actual parameter", ast.V);
 		} else {
 			reportError("var actual parameter not expected here", ast.V);
@@ -538,7 +548,8 @@ public final class Checker implements ActualParameterVisitor<FormalParameter, Vo
 
 	@Override
 	public Void visitMultipleActualParameterSequence(MultipleActualParameterSequence ast, FormalParameterSequence arg) {
-		if (arg instanceof MultipleFormalParameterSequence formals) {
+		if (arg instanceof MultipleFormalParameterSequence) {
+			MultipleFormalParameterSequence formals = (MultipleFormalParameterSequence)arg;
 			ast.AP.visit(this, formals.FP);
 			ast.APS.visit(this, formals.FPS);
 		} else {
@@ -549,7 +560,8 @@ public final class Checker implements ActualParameterVisitor<FormalParameter, Vo
 
 	@Override
 	public Void visitSingleActualParameterSequence(SingleActualParameterSequence ast, FormalParameterSequence arg) {
-		if (arg instanceof SingleFormalParameterSequence formal) {
+		if (arg instanceof SingleFormalParameterSequence) {
+			SingleFormalParameterSequence formal = (SingleFormalParameterSequence)arg;
 			ast.AP.visit(this, formal.FP);
 		} else {
 			reportError("incorrect number of actual parameters", ast);
@@ -592,7 +604,8 @@ public final class Checker implements ActualParameterVisitor<FormalParameter, Vo
 	@Override
 	public TypeDenoter visitSimpleTypeDenoter(SimpleTypeDenoter ast, Void arg) {
 		var binding = ast.I.visit(this);
-		if (binding instanceof TypeDeclaration decl) {
+		if (binding instanceof TypeDeclaration) {
+			TypeDeclaration decl = (TypeDeclaration)binding;
 			return decl.T;
 		}
 
@@ -678,7 +691,8 @@ public final class Checker implements ActualParameterVisitor<FormalParameter, Vo
 	public TypeDenoter visitDotVname(DotVname ast, Void arg) {
 		ast.type = null;
 		var vType = ast.V.visit(this);
-		if (vType instanceof RecordTypeDenoter record) {
+		if (vType instanceof RecordTypeDenoter) {
+			RecordTypeDenoter record = (RecordTypeDenoter)vType;
 			ast.type = checkFieldIdentifier(record.FT, ast.I);
 			checkAndReportError(!ast.type.equals(StdEnvironment.errorType), "no field \"%\" in this record type",
 					ast.I);
@@ -694,9 +708,11 @@ public final class Checker implements ActualParameterVisitor<FormalParameter, Vo
 		ast.type = StdEnvironment.errorType;
 
 		var binding = ast.I.visit(this);
-		if (binding instanceof ConstantDeclaration constant) {
+		if (binding instanceof ConstantDeclaration) {
+			ConstantDeclaration constant = (ConstantDeclaration)binding;
 			return ast.type = constant.getType();
-		} else if (binding instanceof VariableDeclaration variable) {
+		} else if (binding instanceof VariableDeclaration) {
+			VariableDeclaration variable = (VariableDeclaration)binding;
 			return ast.type = variable.getType();
 		}
 
@@ -711,7 +727,8 @@ public final class Checker implements ActualParameterVisitor<FormalParameter, Vo
 
 		var eType = ast.E.visit(this);
 		if (vType != StdEnvironment.errorType) {
-			if (vType instanceof ArrayTypeDenoter arrayType) {
+			if (vType instanceof ArrayTypeDenoter) {
+				ArrayTypeDenoter arrayType = (ArrayTypeDenoter)vType;
 				checkAndReportError(eType.equals(StdEnvironment.integerType), "Integer expression expected here",
 						ast.E);
 				ast.type = arrayType.T;
@@ -796,14 +813,16 @@ public final class Checker implements ActualParameterVisitor<FormalParameter, Vo
 	}
 
 	private static TypeDenoter checkFieldIdentifier(FieldTypeDenoter ast, Identifier I) {
-		if (ast instanceof MultipleFieldTypeDenoter ft) {
+		if (ast instanceof MultipleFieldTypeDenoter) {
+			MultipleFieldTypeDenoter ft = (MultipleFieldTypeDenoter)ast;
 			if (ft.I.spelling.compareTo(I.spelling) == 0) {
 				I.decl = ast;
 				return ft.T;
 			} else {
 				return checkFieldIdentifier(ft.FT, I);
 			}
-		} else if (ast instanceof SingleFieldTypeDenoter ft) {
+		} else if (ast instanceof SingleFieldTypeDenoter) {
+			SingleFieldTypeDenoter ft = (SingleFieldTypeDenoter)ast;
 			if (ft.I.spelling.compareTo(I.spelling) == 0) {
 				I.decl = ast;
 				return ft.T;