code: public static <Vertex> BiDiNavigator<Vertex> reverseBiDiNavigator(BiDiNavigator<Vertex> nav) {
  	return new ReverseBiDiNavigator<Vertex>(nav);
      }
docs: Returns the reverse of a given navigator.  In the resulting
  reverse navigator, the <code>next</code> method returns the
  same result as <code>nav.prev</code>, and the <code>prev</code>
  method returns the same result as <code>nav.next</code>.