public static int height1 (InspectableTree T) {
     int h = 0;
     PositionIterator positer = T.positions();
     while (positer.hasNext()) {
       Position v = positer.nextPosition();
       if (T.isExternal(v))
	 h = Math.max(h, depth(T, v));
     }
     return h;
   }