type level = Fcl_stak.level
val older : level -> level -> bool
val size : unit -> int
val depth : unit -> int
val level : unit -> level
val levels : unit -> level list
val nb_choice_points : unit -> int
exception Level_not_found of level
val cut : level -> unit
exception Fail of string
val fail : string -> 'a
type 'a ref = 'a Fcl_stak.ref
val ref : 'a -> 'a ref
val set : 'a ref -> 'a -> unit
val get : 'a ref -> 'a
type gl = Fcl_stak.gl = { name : string; call : unit -> gl option; }
exception Empty_stack
val reset : unit -> unit
val save : gl list -> level
val backtrack : unit -> gl list
val backtrack_all : unit -> unit
val trail : (unit -> unit) -> unit
val cut_bottom : level -> unit
val unsafe_set : 'a ref -> 'a -> unit