// Textbook fragment 07.14
/**
 * An interface for a binary tree, where each node can have zero, one,
 * or two children.
 */
public interface BinaryTree<E> extends Tree<E> {
  /** Returns the left child of a node. */
  public Position<E> left(Position<E> v)
    throws InvalidPositionException, BoundaryViolationException;
  /** Returns the right child of a node. */
  public Position<E> right(Position<E> v)
    throws InvalidPositionException, BoundaryViolationException;
  /** Returns whether a node has a left child. */
  public boolean hasLeft(Position<E> v) throws InvalidPositionException;
  /** Returns whether a node has a right child. */
  public boolean hasRight(Position<E> v) throws InvalidPositionException;
}