`sig
type elt
type t
val empty : Lwt_pqueue.S.t
val is_empty : Lwt_pqueue.S.t -> bool
val add : Lwt_pqueue.S.elt -> Lwt_pqueue.S.t -> Lwt_pqueue.S.t
val union : Lwt_pqueue.S.t -> Lwt_pqueue.S.t -> Lwt_pqueue.S.t
val find_min : Lwt_pqueue.S.t -> Lwt_pqueue.S.elt
val lookup_min : Lwt_pqueue.S.t -> Lwt_pqueue.S.elt option
val remove_min : Lwt_pqueue.S.t -> Lwt_pqueue.S.t
val size : Lwt_pqueue.S.t -> int
end`