code: GBSNode rightMostChild()
    {
      GBSNode q = this;
      GBSNode p = rightChild();
      while (p != null)
      {
        q = p;
        p = p.rightChild();
      }
      return q;
    }
docs: Find the right-most child of a node by following the paths of
  all of the right-most children all the way to the bottom of
  the tree.