For this reason, the "capacity function" , which does not allow for multiple arcs starting and ending at the same nodes, is sufficient for flow analysis. Similarly, it is enough to impose the "skew symmetry" constraint on flow functions to ensure that flow between two vertices is encoded by a single number (to indicate magnitude), and a sign (to indicate direction) — by knowing the flow between and you implicitly, via skew symmetry, know the flow between and . These simplifications of the model aren't always immediately intuitive, but they are convenient when it comes time to analyze flows.