diff --git a/euler_tour/EulerTour.java b/euler_tour/EulerTour.java
new file mode 100644
index 0000000..ff03cbb
--- /dev/null
+++ b/euler_tour/EulerTour.java
@@ -0,0 +1,41 @@
+package euler_tour;
+
+import tree.binarytree.*;
+import position.Position;
+
+
+
+public abstract class EulerTour<E, R> {
+  protected BinaryTree<E> tree;
+
+  public abstract R execute(BinaryTree<E> T);
+
+  protected void init(BinaryTree<E> T) { tree = T; }
+
+  protected R eulerTour(Position<E> v) {
+    TourResult<R> r = new TourResult<R>();
+    visitLeft(v, r);
+    if (tree.hasLeft(v))
+      r.left = eulerTour(tree.left(v));
+    visitBelow(v, r);
+    if (tree.hasRight(v))
+      r.right = eulerTour(tree.right(v));
+    visitRight(v, r);
+    return r.out;
+  }
+
+  protected void visitLeft(Position<E> v, TourResult<R> r) {}
+
+  protected void visitBelow(Position<E> v, TourResult<R> r) {}
+
+  protected void visitRight(Position<E> v, TourResult<R> r) {}
+
+
+  public class TourResult<R> {
+    public R left;
+    public R right;
+    public R out; 
+  }
+
+}
+
diff --git a/euler_tour/expressions/AdditionOperator.java b/euler_tour/expressions/AdditionOperator.java
new file mode 100644
index 0000000..ed5192b
--- /dev/null
+++ b/euler_tour/expressions/AdditionOperator.java
@@ -0,0 +1,16 @@
+package euler_tour.expressions;
+
+/**
+ * Created with MONSTER.
+ * User: xgiovio
+ * Date: 27/04/2014
+ * Time: 13:08
+ */
+public class AdditionOperator extends ExpressionOperator {
+    public Integer getValue() {
+        return (firstOperand + secondOperand);
+    }
+    public String toString() {
+        return new String("+"); }
+
+}
diff --git a/euler_tour/expressions/EvaluateExpressionTour.java b/euler_tour/expressions/EvaluateExpressionTour.java
new file mode 100644
index 0000000..3803cb7
--- /dev/null
+++ b/euler_tour/expressions/EvaluateExpressionTour.java
@@ -0,0 +1,30 @@
+package euler_tour.expressions;
+
+import euler_tour.EulerTour;
+import position.Position;
+import tree.binarytree.BinaryTree;
+
+/**
+ * Created with MONSTER.
+ * User: xgiovio
+ * Date: 27/04/2014
+ * Time: 13:09
+ */
+public class EvaluateExpressionTour extends EulerTour<ExpressionTerm,Integer> {
+
+    public Integer execute(BinaryTree<ExpressionTerm> T) {
+        init(T);
+        return eulerTour(tree.root());
+    }
+
+    protected void visitRight(Position<ExpressionTerm> v, TourResult<Integer> r) {
+        ExpressionTerm term = v.element();
+        if (tree.isInternal(v)) {
+            ExpressionOperator op = (ExpressionOperator) term;
+            op.setOperands(r.left, r.right);
+        }
+        r.out = term.getValue();
+    }
+}
+
+
diff --git a/euler_tour/expressions/ExpressionOperator.java b/euler_tour/expressions/ExpressionOperator.java
new file mode 100644
index 0000000..9159582
--- /dev/null
+++ b/euler_tour/expressions/ExpressionOperator.java
@@ -0,0 +1,17 @@
+package euler_tour.expressions;
+
+/**
+ * Created with MONSTER.
+ * User: xgiovio
+ * Date: 27/04/2014
+ * Time: 13:07
+ */
+public class ExpressionOperator extends ExpressionTerm {
+
+    protected Integer firstOperand, secondOperand;
+    public void setOperands(Integer x, Integer y) {
+        firstOperand = x;
+        secondOperand = y;
+    }
+
+}
diff --git a/euler_tour/expressions/ExpressionTerm.java b/euler_tour/expressions/ExpressionTerm.java
new file mode 100644
index 0000000..ceb992a
--- /dev/null
+++ b/euler_tour/expressions/ExpressionTerm.java
@@ -0,0 +1,15 @@
+package euler_tour.expressions;
+
+/**
+ * Created with MONSTER.
+ * User: xgiovio
+ * Date: 27/04/2014
+ * Time: 13:06
+ */
+public class ExpressionTerm {
+
+        public Integer getValue() { return 0; }
+        public String toString() {
+            return new String("");
+        }
+}
diff --git a/euler_tour/expressions/ExpressionVariable.java b/euler_tour/expressions/ExpressionVariable.java
new file mode 100644
index 0000000..1dfdee2
--- /dev/null
+++ b/euler_tour/expressions/ExpressionVariable.java
@@ -0,0 +1,18 @@
+package euler_tour.expressions;
+
+/**
+ * Created with MONSTER.
+ * User: xgiovio
+ * Date: 27/04/2014
+ * Time: 13:06
+ */
+public class ExpressionVariable extends ExpressionTerm {
+
+    protected Integer var;
+    public ExpressionVariable(Integer x) { var = x; }
+    public void setVariable(Integer x) { var = x; }
+    public Integer getValue() { return var; }
+    public String toString() { return var.toString(); }
+
+
+}
diff --git a/euler_tour/expressions/StringExpressionTour.java b/euler_tour/expressions/StringExpressionTour.java
new file mode 100644
index 0000000..701c3ab
--- /dev/null
+++ b/euler_tour/expressions/StringExpressionTour.java
@@ -0,0 +1,45 @@
+package euler_tour.expressions;
+
+import euler_tour.EulerTour;
+import position.Position;
+import tree.binarytree.BinaryTree;
+
+/**
+ * Created with MONSTER.
+ * User: xgiovio
+ * Date: 27/04/2014
+ * Time: 13:11
+ */
+public class StringExpressionTour extends EulerTour<ExpressionTerm,String> {
+
+    public String execute(BinaryTree<ExpressionTerm> T) {
+        init(T);
+        return eulerTour(T.root());
+    }
+
+
+
+    protected void visitLeft(Position<ExpressionTerm> v, TourResult<String> r) {
+        if (tree.isInternal(v)) {
+            r.out = new String("(");
+        }else {
+            r.out = new String("");
+        }
+    }
+
+    protected void visitBelow(Position<ExpressionTerm> v, TourResult<String> r) {
+        if (tree.isInternal(v)) {
+            r.out += r.left;
+        }
+        r.out += v.element();
+    }
+
+    protected void visitRight(Position<ExpressionTerm> v,TourResult<String> r) {
+        if (tree.isInternal(v)) {
+            r.out += r.right;
+            r.out += ")";
+        }
+    }
+
+
+}
diff --git a/binarytree/BTNode.java b/tree/binarytree/BTNode.java
similarity index 97%
rename from binarytree/BTNode.java
rename to tree/binarytree/BTNode.java
index 4fa15be..2e0532b 100644
--- a/binarytree/BTNode.java
+++ b/tree/binarytree/BTNode.java
@@ -1,4 +1,4 @@
-package binarytree;
+package tree.binarytree;
 
 public class BTNode<E> implements BTPosition<E> {
 
diff --git a/binarytree/BTPosition.java b/tree/binarytree/BTPosition.java
similarity index 93%
rename from binarytree/BTPosition.java
rename to tree/binarytree/BTPosition.java
index a951bfe..e14711c 100644
--- a/binarytree/BTPosition.java
+++ b/tree/binarytree/BTPosition.java
@@ -1,4 +1,4 @@
-package binarytree;
+package tree.binarytree;
 
 
 import position.Position;
diff --git a/binarytree/BinaryTree.java b/tree/binarytree/BinaryTree.java
similarity index 95%
rename from binarytree/BinaryTree.java
rename to tree/binarytree/BinaryTree.java
index 50f7e57..6bf81d1 100644
--- a/binarytree/BinaryTree.java
+++ b/tree/binarytree/BinaryTree.java
@@ -1,4 +1,4 @@
-package binarytree;
+package tree.binarytree;
 
 
 import exceptions.BoundaryViolationException;
diff --git a/binarytree/LinkedBinaryTree.java b/tree/binarytree/LinkedBinaryTree.java
similarity index 92%
rename from binarytree/LinkedBinaryTree.java
rename to tree/binarytree/LinkedBinaryTree.java
index 13e0381..014ec91 100644
--- a/binarytree/LinkedBinaryTree.java
+++ b/tree/binarytree/LinkedBinaryTree.java
@@ -1,4 +1,4 @@
-package binarytree;
+package tree.binarytree;
 import exceptions.BoundaryViolationException;
 import exceptions.EmptyTreeException;
 import exceptions.InvalidPositionException;
@@ -307,9 +307,29 @@ public class LinkedBinaryTree<E> implements BinaryTree<E> {
       inorderPositions(right(v), pos);
   }
 
+    protected void postorderPositions(Position<E> v, PositionList<Position<E>> pos)    throws InvalidPositionException {
+        if (hasLeft(v))
+            inorderPositions(left(v), pos);
+        if (hasRight(v))
+            inorderPositions(right(v), pos);
+        pos.addLast(v);
+    }
+
 
-    @Override
     public String toString() {
-        return super.toString();
+        String to_return = "";
+        to_return = to_return + "[";
+        if (size() == 0 )
+            return to_return+= "]";
+
+        NodePositionList<Position<E>> t = new NodePositionList<Position<E>>();
+        postorderPositions(root(),t);
+
+        for (Position<E> w :t){
+            to_return+=w.element() + ",";
+        }
+        to_return = to_return.substring(0, to_return.length()-1);
+
+        return to_return+= "]";
     }
 }