code: public void forEachNode(IntProcedure proc, GraphEventType evt) throws ContradictionException {
  		int type;
  		if (evt == GraphEventType.REMOVE_NODE) {
  			type = GraphDelta.NR;
  			for (int i = frozenFirst[type]; i < frozenLast[type]; i++) {
  				if (delta.getCause(i, type) != propagator) {
  					proc.execute(delta.get(i, type));
  				}
  			}
  		} else if (evt == GraphEventType.ADD_NODE) {
  			type = GraphDelta.NE;
  			for (int i = frozenFirst[type]; i < frozenLast[type]; i++) {
  				if (delta.getCause(i, type) != propagator) {
  					proc.execute(delta.get(i, type));
  				}
  			}
  		} else {
  			throw new UnsupportedOperationException();
  		}
  	}
docs: Applies proc to every vertex which has just been removed or enforced, depending on evt.
  @param proc    an incremental procedure over vertices
  @param evt    either ENFORCENODE or REMOVENODE
  @throws ContradictionException if a failure occurs