val fold : (M.key list -> 'a -> 'b -> 'b) -> 'a t -> 'b -> 'b
val compare : ('a -> 'a -> int) -> 'a t -> 'a t -> int
val equal : ('a -> 'a -> bool) -> 'a t -> 'a t -> bool
val fold : (M.key list -> 'a -> 'b -> 'b) -> 'a t -> 'b -> 'b
val compare : ('a -> 'a -> int) -> 'a t -> 'a t -> int
val equal : ('a -> 'a -> bool) -> 'a t -> 'a t -> bool