code: public Graph<K, VV, EV> difference(Graph<K, VV, EV> graph) {
  		DataSet<Vertex<K, VV>> removeVerticesData = graph.getVertices();
  		return this.removeVertices(removeVerticesData);
  	}
docs: Performs Difference on the vertex and edge sets of the input graphs
  removes common vertices and edges. If a source/target vertex is removed,
  its corresponding edge will also be removed
  
  @param graph the graph to perform difference with
  @return a new graph where the common vertices and edges have been removed