public void addEdge(T a, T b) {
		//System.out.println("add edge "+a+" to "+b);
		Node<T> a_node = getNode(a);
		Node<T> b_node = getNode(b);
		a_node.addEdge(b_node);
	}
Map from node payload to node containing it
tool/src/org/antlr/v4/misc/Graph.java