class ['a] ograph2way :
  (< add : 'a * 'a Oset.oset -> 'c; delkey : 'a -> 'c;
   find : 'a -> 'a Oset.oset; iter : ('a * 'd -> unit) -> 'e;
   replkey : 'a * 'a Oset.oset -> 'c; .. >
     as 'c) ->
  (< add : 'a * 'a Oset.oset -> 'f; delkey : 'a -> 'f;
   find : 'a -> 'a Oset.oset; replkey : 'a * 'a Oset.oset -> 'f; .. >
     as 'f) ->
  (unit -> 'a Oset.oset) ->
object ('o)
  inherit ['a] Ograph.ograph
  val pred : 'f
  val succ : 'c

  (* ograph concrete instantiation of virtual methods *)
  method empty : 'o

  method add_node : 'a -> 'o
  method del_node : 'a -> 'o

  method add_arc : 'a * 'a -> 'o
  method del_arc : 'a * 'a -> 'o

  method nodes : 'a Oset.oset
  method predecessors : 'a -> 'a Oset.oset
  method successors : 'a -> 'a Oset.oset

  method ancestors : 'a Oset.oset -> 'a Oset.oset
  method brothers : 'a -> 'a Oset.oset
  method children : 'a Oset.oset -> 'a Oset.oset

end