val is_empty : 'a t -> bool
val mem : key -> 'a t -> bool
val add : key -> 'a -> 'a t -> 'a t
val remove : key -> 'a t -> 'a t
val find : key -> 'a t -> 'a
val max_binding : 'a t -> key * 'a
val find_first_opt : (key -> bool) -> 'a t -> (key * 'a) option