object CI {
  trait TreeDisplay {
        type TreeNode <: ITreeNode;
        trait ITreeNode {
          def display(): unit;
        }
  }
  trait TreeDisplayExp {
        def getRoot(): TreeNode;
        type TreeNode <: ITreeNodeExp;
        trait ITreeNodeExp {}
  }
  trait TreeDisplayFinal extends TreeDisplay with TreeDisplayExp {
        type TreeNode <: ITreeNode with ITreeNodeExp;
  }
  abstract class SimpleTreeDisplay: TreeDisplayFinal extends TreeDisplay {
    def display() = { this.getRoot().display(); }
  }
}