code: public static <V> ForwardNavigator<V> unionFwdNav(final ForwardNavigator<V> fn1,
  						      final ForwardNavigator<V> fn2) {
  	return new ForwardNavigator<V>() {
  	    public List<V> next(V v) {
  		return DSUtil.unionList(fn1.next(v), fn2.next(v));
  	    }
  	};
      }
docs: Unions two <code>ForwardNavigator</code>.  For each vertex
  <code>v</code>, successors indicated by the union navigator
  consist of all the successors indicated by <code>fn1</code>,
  followed by all the successors indicated by <code>fn2</code>.
  Note that the same successors may be indicated twice, once by
  <code>fn1</code> and once by <code>fn2</code>.