sig
type t
val empty : Letify.Defs.t
val merge : Letify.Defs.t -> Letify.Defs.t -> Letify.Defs.t
val extract : Lang.F.pred -> Letify.Defs.t
val add : Letify.Defs.t Pervasives.ref -> Lang.F.pred -> unit
val domain : Letify.Defs.t -> Lang.F.Vars.t
end