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