`sig
type t
external of_string : string -> Var.t = "camlidl_var_ap_var_of_string"
external compare : Var.t -> Var.t -> int = "camlidl_var_ap_var_compare"
external to_string : Var.t -> string = "camlidl_var_ap_var_to_string"
external hash : Var.t -> int = "camlidl_var_ap_var_hash"
val print : Stdlib.Format.formatter -> Var.t -> unit
external set_var_operations : unit -> unit
= "camlidl_apron_set_var_operations"
end`