/** Node of a binary tree */
public class BTNode implements Position {
  private Object element;
  private BTNode left, right, parent;
  /** default constructor */
  public BTNode() { }
  /** constructor with parameters */
  public BTNode(Object o, BTNode u, BTNode v, BTNode w) {
    setElement(o);
    setParent(u);
    setLeft(v);
    setRight(w);
  }
  public Object element() { return element; }
  public void setElement(Object o) { element=o; }
  public BTNode getLeft() { return left; }
  public void setLeft(BTNode v) { left=v; }
  public BTNode getRight() { return right; }
  public void setRight(BTNode v) { right=v; }
  public BTNode getParent() { return parent; }
  public void setParent(BTNode v) { parent=v; }
}