sig
type level
val older : Facile.Stak.level -> Facile.Stak.level -> bool
val size : unit -> int
val depth : unit -> int
val level : unit -> Facile.Stak.level
val levels : unit -> Facile.Stak.level list
val nb_choice_points : unit -> int
exception Level_not_found of Facile.Stak.level
val cut : Facile.Stak.level -> unit
exception Fail of string
val fail : string -> 'a
val trail : (unit -> unit) -> unit
type 'a ref
val ref : 'a -> 'a Facile.Stak.ref
val set : 'a Facile.Stak.ref -> 'a -> unit
val get : 'a Facile.Stak.ref -> 'a
end