private void CheckRep() throws RuntimeException{
		for (Node n: nodes){
			if (n.getLabel() == null){
				throw new RuntimeException("Node label is null");
			}
		}
		for (Edge e: edges){
			if (e.getLabel() == null){
				throw new RuntimeException("Edge Label is null");
			}
			if (e.getStartNode() == null){
				throw new RuntimeException("Start Node is null");
			}
			if (e.getEndNode() == null){
				throw new RuntimeException("End Node is null");
			}
		}
	}