sig
type key1
type key2
val mem : Wprop.Indexed2.key1 -> Wprop.Indexed2.key2 -> bool
val property : Wprop.Indexed2.key1 -> Wprop.Indexed2.key2 -> Property.t
val add_hook :
(Wprop.Indexed2.key1 -> Wprop.Indexed2.key2 -> Property.t -> unit) ->
unit
end