    sig
      val length : 'a list -> int
      val hd : 'a list -> 'a
      val tl : 'a list -> 'a list
      val nth : 'a list -> int -> 'a
      val rev : 'a list -> 'a list
      val append : 'a list -> 'a list -> 'a list
      val rev_append : 'a list -> 'a list -> 'a list
      val concat : 'a list list -> 'a list
      val flatten : 'a list list -> 'a list
      val iter : f:('a -> unit) -> 'a list -> unit
      val map : f:('a -> 'b) -> 'a list -> 'b list
      val rev_map : f:('a -> 'b) -> 'a list -> 'b list
      val fold_left : f:('a -> 'b -> 'a) -> init:'a -> 'b list -> 'a
      val fold_right : f:('a -> 'b -> 'b) -> 'a list -> init:'b -> 'b
      val iter2 : f:('a -> 'b -> unit) -> 'a list -> 'b list -> unit
      val map2 : f:('a -> 'b -> 'c) -> 'a list -> 'b list -> 'c list
      val rev_map2 : f:('a -> 'b -> 'c) -> 'a list -> 'b list -> 'c list
      val fold_left2 :
        f:('a -> 'b -> 'c -> 'a) -> init:'a -> 'b list -> 'c list -> 'a
      val fold_right2 :
        f:('a -> 'b -> 'c -> 'c) -> 'a list -> 'b list -> init:'c -> 'c
      val for_all : f:('a -> bool) -> 'a list -> bool
      val exists : f:('a -> bool) -> 'a list -> bool
      val for_all2 : f:('a -> 'b -> bool) -> 'a list -> 'b list -> bool
      val exists2 : f:('a -> 'b -> bool) -> 'a list -> 'b list -> bool
      val mem : 'a -> set:'a list -> bool
      val memq : 'a -> set:'a list -> bool
      val find : f:('a -> bool) -> 'a list -> 'a
      val filter : f:('a -> bool) -> 'a list -> 'a list
      val find_all : f:('a -> bool) -> 'a list -> 'a list
      val partition : f:('a -> bool) -> 'a list -> 'a list * 'a list
      val assoc : 'a -> ('a * 'b) list -> 'b
      val assq : 'a -> ('a * 'b) list -> 'b
      val mem_assoc : 'a -> map:('a * 'b) list -> bool
      val mem_assq : 'a -> map:('a * 'b) list -> bool
      val remove_assoc : 'a -> ('a * 'b) list -> ('a * 'b) list
      val remove_assq : 'a -> ('a * 'b) list -> ('a * 'b) list
      val split : ('a * 'b) list -> 'a list * 'b list
      val combine : 'a list -> 'b list -> ('a * 'b) list
      val sort : cmp:('a -> 'a -> int) -> 'a list -> 'a list
      val stable_sort : cmp:('a -> 'a -> int) -> 'a list -> 'a list
    end