Not sure if this is the best choice. The alternative is to have 4 functions `maximum_flow_value`, `maximum_flow`, `minimum_cut_value` and `minimum_cut` as @ysitu proposed above. I think this is clearer but it is not backwards compatible because until now `max_flow/min_cut` only returned the flow value. I'm not opposed to break backwards compatibility in order to have a better interface, so if there is consensus (or there is not strong opposition to this) I'll make the changes.