diff --git a/ws2011/Compiler I/Uebungen/2. Uebung/solution/ConstantFolding.java b/ws2011/Compiler I/Uebungen/2. Uebung/solution/ConstantFolding.java
new file mode 100644
index 00000000..dd0047b4
--- /dev/null
+++ b/ws2011/Compiler I/Uebungen/2. Uebung/solution/ConstantFolding.java	
@@ -0,0 +1,523 @@
+/*
+ * To change this template, choose Tools | Templates
+ * and open the template in the editor.
+ */
+package solution;
+import Triangle.AbstractSyntaxTrees.AnyTypeDenoter;
+import Triangle.AbstractSyntaxTrees.ArrayExpression;
+import Triangle.AbstractSyntaxTrees.ArrayTypeDenoter;
+import Triangle.AbstractSyntaxTrees.AssignCommand;
+import Triangle.AbstractSyntaxTrees.BinaryExpression;
+import Triangle.AbstractSyntaxTrees.BinaryOperatorDeclaration;
+import Triangle.AbstractSyntaxTrees.BoolTypeDenoter;
+import Triangle.AbstractSyntaxTrees.CallCommand;
+import Triangle.AbstractSyntaxTrees.CallExpression;
+import Triangle.AbstractSyntaxTrees.CharTypeDenoter;
+import Triangle.AbstractSyntaxTrees.CharacterExpression;
+import Triangle.AbstractSyntaxTrees.CharacterLiteral;
+import Triangle.AbstractSyntaxTrees.ConstActualParameter;
+import Triangle.AbstractSyntaxTrees.ConstDeclaration;
+import Triangle.AbstractSyntaxTrees.ConstFormalParameter;
+import Triangle.AbstractSyntaxTrees.DotVname;
+import Triangle.AbstractSyntaxTrees.EmptyActualParameterSequence;
+import Triangle.AbstractSyntaxTrees.EmptyCommand;
+import Triangle.AbstractSyntaxTrees.EmptyExpression;
+import Triangle.AbstractSyntaxTrees.EmptyFormalParameterSequence;
+import Triangle.AbstractSyntaxTrees.ErrorTypeDenoter;
+import Triangle.AbstractSyntaxTrees.Expression;
+import Triangle.AbstractSyntaxTrees.FuncActualParameter;
+import Triangle.AbstractSyntaxTrees.FuncDeclaration;
+import Triangle.AbstractSyntaxTrees.FuncFormalParameter;
+import Triangle.AbstractSyntaxTrees.Identifier;
+import Triangle.AbstractSyntaxTrees.IfCommand;
+import Triangle.AbstractSyntaxTrees.IfExpression;
+import Triangle.AbstractSyntaxTrees.IntTypeDenoter;
+import Triangle.AbstractSyntaxTrees.IntegerExpression;
+import Triangle.AbstractSyntaxTrees.IntegerLiteral;
+import Triangle.AbstractSyntaxTrees.LetCommand;
+import Triangle.AbstractSyntaxTrees.LetExpression;
+import Triangle.AbstractSyntaxTrees.MultipleActualParameterSequence;
+import Triangle.AbstractSyntaxTrees.MultipleArrayAggregate;
+import Triangle.AbstractSyntaxTrees.MultipleFieldTypeDenoter;
+import Triangle.AbstractSyntaxTrees.MultipleFormalParameterSequence;
+import Triangle.AbstractSyntaxTrees.MultipleRecordAggregate;
+import Triangle.AbstractSyntaxTrees.Operator;
+import Triangle.AbstractSyntaxTrees.ProcActualParameter;
+import Triangle.AbstractSyntaxTrees.ProcDeclaration;
+import Triangle.AbstractSyntaxTrees.ProcFormalParameter;
+import Triangle.AbstractSyntaxTrees.Program;
+import Triangle.AbstractSyntaxTrees.RecordExpression;
+import Triangle.AbstractSyntaxTrees.RecordTypeDenoter;
+import Triangle.AbstractSyntaxTrees.SequentialCommand;
+import Triangle.AbstractSyntaxTrees.SequentialDeclaration;
+import Triangle.AbstractSyntaxTrees.SimpleTypeDenoter;
+import Triangle.AbstractSyntaxTrees.SimpleVname;
+import Triangle.AbstractSyntaxTrees.SingleActualParameterSequence;
+import Triangle.AbstractSyntaxTrees.SingleArrayAggregate;
+import Triangle.AbstractSyntaxTrees.SingleFieldTypeDenoter;
+import Triangle.AbstractSyntaxTrees.SingleFormalParameterSequence;
+import Triangle.AbstractSyntaxTrees.SingleRecordAggregate;
+import Triangle.AbstractSyntaxTrees.SubscriptVname;
+import Triangle.AbstractSyntaxTrees.TypeDeclaration;
+import Triangle.AbstractSyntaxTrees.UnaryExpression;
+import Triangle.AbstractSyntaxTrees.UnaryOperatorDeclaration;
+import Triangle.AbstractSyntaxTrees.VarActualParameter;
+import Triangle.AbstractSyntaxTrees.VarDeclaration;
+import Triangle.AbstractSyntaxTrees.VarFormalParameter;
+import Triangle.AbstractSyntaxTrees.Visitor;
+import Triangle.AbstractSyntaxTrees.VnameExpression;
+import Triangle.AbstractSyntaxTrees.WhileCommand;
+import Triangle.StdEnvironment;
+import Triangle.SyntacticAnalyzer.SourcePosition;
+
+/**
+ *
+ * @author Michael
+ */
+public class ConstantFolding implements Visitor{
+    
+    
+    
+         /**
+	 * Returns <code>true</code> if the given expression represents constant value.
+	 * This value can be a boolean or integer.
+	 * @param e the expression to test
+	 * @return <code>true</code> if the given expression represents constant value
+	 */
+	private boolean isConstant(Expression e) {
+		if(e instanceof IntegerExpression)
+			return true;
+		if(e instanceof VnameExpression) {
+			VnameExpression vname = (VnameExpression)e;
+			if(vname.V instanceof SimpleVname)
+				if(((SimpleVname)vname.V).I.spelling.equals(StdEnvironment.trueDecl.I.spelling) 
+						|| ((SimpleVname)vname.V).I.spelling.equals(StdEnvironment.falseDecl.I.spelling))
+					return true;
+		}
+		return false;
+	}
+	
+	/**
+	 * Returns the boolean value of the given expression that represents a boolean value.
+	 * @param e a boolean value
+	 * @return the boolean value of the given expression that represents a boolean value
+	 */
+	private boolean parseBoolean(Expression e) {
+		if(e instanceof VnameExpression) {
+			VnameExpression vname = (VnameExpression)e;
+			if(vname.V instanceof SimpleVname)
+				if(((SimpleVname)vname.V).I.spelling.equals(StdEnvironment.trueDecl.I.spelling))
+					return true;
+				if(((SimpleVname)vname.V).I.spelling.equals(StdEnvironment.falseDecl.I.spelling))
+					return false;
+		}
+		throw new RuntimeException();
+	}
+	
+	/**
+	 * Returns an expression representing the given boolean value.
+	 * @param val the boolean value that will be represented by the returned expression
+	 * @return an expression representing the given boolean value
+	 */
+	private Expression createBoolean(boolean val) {
+		Identifier iAST = new Identifier(val ? "true" : "false", new SourcePosition());
+		iAST.decl = val ? StdEnvironment.trueDecl : StdEnvironment.falseDecl;
+		SimpleVname vAST = new SimpleVname(iAST, new SourcePosition());
+		vAST.type = StdEnvironment.booleanType;
+		VnameExpression boolExpression = new VnameExpression(vAST, new SourcePosition());
+		return boolExpression;
+	}
+
+        
+        private Expression createInteger(int i){
+            return new IntegerExpression(new IntegerLiteral(String.valueOf(i),null), null);
+        }
+       
+    @Override
+    public Object visitBinaryExpression(BinaryExpression ast, Object o) {
+        
+        boolean e1 = false;
+        boolean e2 = false;
+        if(isConstant(ast.E1)){
+            //optimize E
+            try{
+                boolean b = parseBoolean(ast.E1);
+                ast.E1 = createBoolean(b);
+
+
+            } catch (RuntimeException e)
+            {
+                ast.E1 = (IntegerExpression)ast.E1;
+             
+            }
+            e1 = true;
+        }
+
+        if(isConstant(ast.E2)){
+            //optimize E
+            try{
+                boolean b = parseBoolean(ast.E2);
+                ast.E2 = createBoolean(b);
+
+            } catch (RuntimeException e)
+            {
+                ast.E2 = (IntegerExpression)ast.E2;
+
+            }
+            e2 = true;
+        }
+
+        if(e1 & e2) {
+            if(ast.O.spelling.equals("+")){
+                return createInteger( ast.E1.GETVALUE() + ast.E2.GETVALUE());
+               
+            }else if(ast.O.spelling.equals("<")){
+                
+                return createBoolean(ast.E1.GETVALUE() < ast.E2.GETVALUE());
+            }else if(ast.O.spelling.equals("-")){
+                
+                //....
+                
+            } 
+            
+            //Instead define a Operator which can execute itself:
+            return ast.O(ast.E1,ast.E2);
+
+        }
+
+        return ast;
+        
+    }
+
+    @Override
+    public Object visitUnaryExpression(UnaryExpression ast, Object o) {
+        
+        boolean e1 = false;
+        if(isConstant(ast.E)){
+            //optimize E
+            try{
+                boolean b = parseBoolean(ast.E);
+                ast.E = createBoolean(b);
+                if(ast.O.spelling.equals("\\")){
+                    return createBoolean(!b);
+                }
+
+            } catch (RuntimeException e)
+            {
+                ast.E = (IntegerExpression)ast.E;
+            }
+   
+        }
+        
+        return ast;
+    }
+
+
+
+
+
+    
+    @Override
+    public Object visitBinaryOperatorDeclaration(BinaryOperatorDeclaration ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitUnaryOperatorDeclaration(UnaryOperatorDeclaration ast, Object o) {
+        return null; // not of interest
+    }
+
+
+    
+        
+    @Override
+    public Object visitAssignCommand(AssignCommand ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitCallCommand(CallCommand ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitEmptyCommand(EmptyCommand ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitIfCommand(IfCommand ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitLetCommand(LetCommand ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitSequentialCommand(SequentialCommand ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitWhileCommand(WhileCommand ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitArrayExpression(ArrayExpression ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitCallExpression(CallExpression ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitCharacterExpression(CharacterExpression ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitEmptyExpression(EmptyExpression ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitIfExpression(IfExpression ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitIntegerExpression(IntegerExpression ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitLetExpression(LetExpression ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitRecordExpression(RecordExpression ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitVnameExpression(VnameExpression ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitConstDeclaration(ConstDeclaration ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitFuncDeclaration(FuncDeclaration ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitProcDeclaration(ProcDeclaration ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitSequentialDeclaration(SequentialDeclaration ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitTypeDeclaration(TypeDeclaration ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitVarDeclaration(VarDeclaration ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitMultipleArrayAggregate(MultipleArrayAggregate ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitSingleArrayAggregate(SingleArrayAggregate ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitMultipleRecordAggregate(MultipleRecordAggregate ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitSingleRecordAggregate(SingleRecordAggregate ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitConstFormalParameter(ConstFormalParameter ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitFuncFormalParameter(FuncFormalParameter ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitProcFormalParameter(ProcFormalParameter ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitVarFormalParameter(VarFormalParameter ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitEmptyFormalParameterSequence(EmptyFormalParameterSequence ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitMultipleFormalParameterSequence(MultipleFormalParameterSequence ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitSingleFormalParameterSequence(SingleFormalParameterSequence ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitConstActualParameter(ConstActualParameter ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitFuncActualParameter(FuncActualParameter ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitProcActualParameter(ProcActualParameter ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitVarActualParameter(VarActualParameter ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitEmptyActualParameterSequence(EmptyActualParameterSequence ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitMultipleActualParameterSequence(MultipleActualParameterSequence ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitSingleActualParameterSequence(SingleActualParameterSequence ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitAnyTypeDenoter(AnyTypeDenoter ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitArrayTypeDenoter(ArrayTypeDenoter ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitBoolTypeDenoter(BoolTypeDenoter ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitCharTypeDenoter(CharTypeDenoter ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitErrorTypeDenoter(ErrorTypeDenoter ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitSimpleTypeDenoter(SimpleTypeDenoter ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitIntTypeDenoter(IntTypeDenoter ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitRecordTypeDenoter(RecordTypeDenoter ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitMultipleFieldTypeDenoter(MultipleFieldTypeDenoter ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitSingleFieldTypeDenoter(SingleFieldTypeDenoter ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitCharacterLiteral(CharacterLiteral ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitIdentifier(Identifier ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitIntegerLiteral(IntegerLiteral ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitOperator(Operator ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitDotVname(DotVname ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitSimpleVname(SimpleVname ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitSubscriptVname(SubscriptVname ast, Object o) {
+        return null; // not of interest
+    }
+
+    @Override
+    public Object visitProgram(Program ast, Object o) {
+        return null; // not of interest
+    }
+    
+}
diff --git a/ws2011/Compiler I/Uebungen/2. Uebung/solution/SymbolTable.java b/ws2011/Compiler I/Uebungen/2. Uebung/solution/SymbolTable.java
new file mode 100644
index 00000000..61f78816
--- /dev/null
+++ b/ws2011/Compiler I/Uebungen/2. Uebung/solution/SymbolTable.java	
@@ -0,0 +1,72 @@
+package Triangle.ContextualAnalyzer;
+
+import java.util.List;
+import java.util.Map;
+import java.util.Stack;
+
+import Triangle.AbstractSyntaxTrees.Declaration;
+import java.util.ArrayList;
+import java.util.HashMap;
+
+public final class SymbolTable {
+
+  private Map<String, Stack<Declaration>> symtab;
+  private List<List<String>> scopeStack;
+
+  public SymbolTable () {
+      symtab = new HashMap<String, Stack<Declaration>>();
+      scopeStack = new ArrayList<List<String>>();
+  }
+
+  // Opens a new level in the identification table, 1 higher than the
+  // current topmost level.
+  public void openScope () {
+        // new empty list
+	scopeStack.add(new ArrayList<String>());
+  }
+
+  // Closes the topmost level in the identification table, discarding
+  // all entries belonging to that level.
+  public void closeScope () {
+      //delete from symtab
+      for(int i = 0; i < scopeStack.get(scopeStack.size() -1).size(); i++){
+         if(symtab.containsKey(scopeStack.get(scopeStack.size() -1).get(i))){
+             symtab.get(scopeStack.get(scopeStack.size() -1).get(i)).pop();
+             if(symtab.get(scopeStack.get(scopeStack.size() -1).get(i)).empty()){
+                 symtab.remove(scopeStack.get(scopeStack.size() -1).get(i));
+             }
+         }
+      }
+      // delete top list
+      scopeStack.remove(scopeStack.size()-1);
+  }
+
+  // Makes a new entry in the identification table for the given identifier
+  // and attribute. The new entry belongs to the current level.
+  // duplicated is set to to true if there is already an entry for the
+  // same identifier at the current level.
+  public void enter (String id, Declaration attr) {
+      scopeStack.get(scopeStack.size()-1).add(id);
+      if(symtab.containsKey(id)){
+          symtab.get(id).push(attr);
+      }else{
+          symtab.put(id, new Stack<Declaration>());
+          symtab.get(id).push(attr);
+      }
+  }
+
+  // Finds an entry for the given identifier in the identification table,
+  // if any. If there are several entries for that identifier, finds the
+  // entry at the highest level, in accordance with the scope rules.
+  // Returns null if no entry is found.
+  // otherwise returns the attribute field of the entry found.
+  public Declaration retrieve (String id) {
+	
+      if(symtab.containsKey(id)){
+          return symtab.get(id).firstElement();
+      }
+         
+      return null;
+  }
+
+}
diff --git a/ws2011/Compiler I/Uebungen/2. Uebung/solution/solution.odt b/ws2011/Compiler I/Uebungen/2. Uebung/solution/solution.odt
new file mode 100644
index 00000000..93e5f3df
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