val mem_vertex : PV.t -> t -> bool
val iter_edges : (PV.t -> PV.t -> unit) -> t -> unit
val fold_edges : (PV.t -> PV.t -> 'a -> 'a) -> t -> 'a -> 'a
val iter_edges_e : (PE.t -> unit) -> t -> unit
val fold_edges_e : (PE.t -> 'a -> 'a) -> t -> 'a -> 'a