`type t = Graph__Imperative.Digraph.ConcreteBidirectional(PkgV).t`
`module V : sig ... end`
`type vertex = V.t`
`module E : sig ... end`
`type edge = E.t`
`val is_directed : bool`
`val is_empty : t -> bool`
`val nb_vertex : t -> int`
`val nb_edges : t -> int`
`val out_degree : t -> vertex -> int`
`val in_degree : t -> vertex -> int`
`val mem_vertex : t -> vertex -> bool`
`val mem_edge : t -> vertex -> vertex -> bool`
`val mem_edge_e : t -> edge -> bool`
`val find_edge : t -> vertex -> vertex -> edge`
`val find_all_edges : t -> vertex -> vertex -> edge list`
`val succ : t -> vertex -> vertex list`
`val pred : t -> vertex -> vertex list`
`val succ_e : t -> vertex -> edge list`
`val pred_e : t -> vertex -> edge list`
`val iter_vertex : (vertex -> unit) -> t -> unit`
`val fold_vertex : (vertex -> 'a -> 'a) -> t -> 'a -> 'a`
`val iter_edges : (vertex -> vertex -> unit) -> t -> unit`
`val fold_edges : (vertex -> vertex -> 'a -> 'a) -> t -> 'a -> 'a`
`val iter_edges_e : (edge -> unit) -> t -> unit`
`val fold_edges_e : (edge -> 'a -> 'a) -> t -> 'a -> 'a`
`val map_vertex : (vertex -> vertex) -> t -> t`
`val iter_succ : (vertex -> unit) -> t -> vertex -> unit`
`val iter_pred : (vertex -> unit) -> t -> vertex -> unit`
`val fold_succ : (vertex -> 'a -> 'a) -> t -> vertex -> 'a -> 'a`
`val fold_pred : (vertex -> 'a -> 'a) -> t -> vertex -> 'a -> 'a`
`val iter_succ_e : (edge -> unit) -> t -> vertex -> unit`
`val fold_succ_e : (edge -> 'a -> 'a) -> t -> vertex -> 'a -> 'a`
`val iter_pred_e : (edge -> unit) -> t -> vertex -> unit`
`val fold_pred_e : (edge -> 'a -> 'a) -> t -> vertex -> 'a -> 'a`
`val create : ?size:int -> unit -> t`
`val clear : t -> unit`
`val copy : t -> t`
`val add_vertex : t -> vertex -> unit`
`val remove_vertex : t -> vertex -> unit`
`val add_edge : t -> vertex -> vertex -> unit`
`val add_edge_e : t -> edge -> unit`
`val remove_edge : t -> vertex -> vertex -> unit`
`val remove_edge_e : t -> edge -> unit`