diff --git a/sources/zweic/Tree.scala b/sources/zweic/Tree.scala
new file mode 100755
index 0000000..123fdcf
--- /dev/null
+++ b/sources/zweic/Tree.scala
@@ -0,0 +1,159 @@
+/*  zweic -- a compiler for zwei
+ *
+ *  Stephane Micheloud & LAMP
+ *
+ *  $Id$
+ */
+
+package zweic;
+
+import Operators.Operator;
+
+//############################################################################
+// The root of the tree node hierarchy
+
+/**
+ * Class Tree defines the type of all abstract syntax tree nodes.
+ */
+abstract class Tree {
+
+  /**
+   * The source code position of this tree node.
+   * Has to be set explicitly woth the setPos method
+   */
+  private var p: Int = Position.UNDEFINED;
+  def pos: Int = p;
+  def setPos(p: Int): this.type = { this.p = p; this }
+
+}
+
+//############################################################################
+// Tree node representing a complete program
+
+/**
+ * P = Program { D } E
+ */
+case class Program(classes: List[ClassDef], main: Expr)
+     extends Tree;
+
+//############################################################################
+// Tree nodes for definitions
+
+/**
+ * A common superclass for all definitions
+ */
+abstract class Def extends Tree {
+  def name: Name;
+}
+
+/**
+ * D = ClassDef name [ name ] { M }
+ */
+case class ClassDef(
+// ... � compl�ter ...
+                   )
+     extends Def;
+
+
+/**
+ * A common superclass for member definitions
+ */
+abstract class Member extends Def;
+
+/**
+ * M = FieldDecl name T
+ */
+case class FieldDecl(
+// ... � compl�ter ...
+                    )
+     extends Member;
+
+
+/**
+ * D = MethodDecl name name { name T } T E
+ */
+case class MethodDef(
+// ... � compl�ter ...
+                    )
+     extends Member;
+
+//############################################################################
+// Tree nodes for types
+
+/**
+ * A common superclass for tree nodes designating types
+ */
+abstract class TypeTree extends Tree;
+
+/**
+ * T = Int
+ */
+case class IntType extends TypeTree;
+
+/**
+ * T = Null
+ */
+case class NullType extends TypeTree;
+
+/**
+ * T = ClassType name
+ */
+case class ClassType(name: Name) extends TypeTree;
+
+//############################################################################
+// Tree nodes for statements
+
+/**
+ * A common superclass for all statements
+ */
+abstract class Stat extends Tree;
+
+/**
+ * S = While E { S }
+ */
+case class While(cond: Expr, stats: List[Stat]) extends Stat;
+
+/**
+ * S = Var name T E
+ */
+case class Var(varname: Name, vartype: TypeTree, init: Expr)
+     extends Stat;
+
+/**
+ * S = Set name E
+ */
+case class Set(name: Name, expr: Expr) extends Stat;
+
+/**
+ * S = Do E
+ */
+case class Do(expr: Expr) extends Stat;
+
+/**
+ * S = PrintInt E
+ */
+case class PrintInt(expr: Expr) extends Stat;
+
+/**
+ * S = PrintChar E
+ */
+case class PrintChar(expr: Expr) extends Stat;
+
+//############################################################################
+// Tree nodes for expressions
+
+/**
+ * A common superclass for expressions
+ */
+abstract class Expr extends Tree;
+
+// ... � compl�ter ...
+
+/**
+ * E = Unop O E
+ */
+case class Unop(op: Operator, expr: Expr) extends Expr;
+
+// ... � compl�ter ...
+
+//############################################################################