plus
Returns a new Graph, with node added to it. Note: as currently implemented, if node already belongs to this graph, its existing outgoing edges are discarded in the result rather than preserved.
Returns a new Graph, with edge added to it (implicitly adding its endpoints, if missing). Note: as currently implemented, any other outgoing edge that edge.source already had in this graph is discarded in the result, rather than kept alongside edge (unlike MutableGraph.add, which merges the new edge in without discarding existing ones).