`sig
type t = (int * int) BatAvlTree.tree
type elt = int
val empty : t
val is_empty : t -> bool
val mem : int -> t -> bool
val add : int -> t -> t
val add_range : int -> int -> t -> t
val singleton : int -> t
val remove : int -> t -> t
val remove_range : int -> int -> t -> t
val union : t -> t -> t
val inter : t -> t -> t
val diff : t -> t -> t
val compl : t -> t
val compare : t -> t -> int
val equal : t -> t -> bool
val ord : t -> t -> BatOrd.order
val subset : t -> t -> bool
val from : int -> t -> t
val after : int -> t -> t
val until : int -> t -> t
val before : int -> t -> t
val iter : (int -> unit) -> t -> unit
val iter_range : (int -> int -> unit) -> t -> unit
val fold : (int -> 'a -> 'a) -> t -> 'a -> 'a
val fold_range : (int -> int -> 'a -> 'a) -> t -> 'a -> 'a
val for_all : (int -> bool) -> t -> bool
val exists : (int -> bool) -> t -> bool
val filter : (int -> bool) -> t -> t
val partition : (int -> bool) -> t -> t * t
val cardinal : t -> int
val elements : t -> int list
val ranges : t -> (int * int) list
val min_elt : t -> int
val max_elt : t -> int
val choose : t -> int
val enum : t -> (int * int) BatEnum.t
val of_enum : (int * int) BatEnum.t -> t
val of_list : (int * int) list -> t
val print : 'a BatIO.output -> t -> unit
end`