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 : ('a -> unit) -> 'a list -> unit
  val map : ('a -> 'b) -> 'a list -> 'b list
  val rev_map : ('a -> 'b) -> 'a list -> 'b list
  val fold_left : ('a -> 'b -> 'a) -> 'a -> 'b list -> 'a
  val fold_right : ('a -> 'b -> 'b) -> 'a list -> 'b -> 'b
  val iter2 : ('a -> 'b -> unit) -> 'a list -> 'b list -> unit
  val map2 : ('a -> 'b -> 'c) -> 'a list -> 'b list -> 'c list
  val rev_map2 : ('a -> 'b -> 'c) -> 'a list -> 'b list -> 'c list
  val fold_left2 : ('a -> 'b -> 'c -> 'a) -> 'a -> 'b list -> 'c list -> 'a
  val fold_right2 : ('a -> 'b -> 'c -> 'c) -> 'a list -> 'b list -> 'c -> 'c
  val for_all : ('a -> bool) -> 'a list -> bool
  val exists : ('a -> bool) -> 'a list -> bool
  val for_all2 : ('a -> 'b -> bool) -> 'a list -> 'b list -> bool
  val exists2 : ('a -> 'b -> bool) -> 'a list -> 'b list -> bool
  val mem : 'a -> 'a list -> bool
  val memq : 'a -> 'a list -> bool
  val find : ('a -> bool) -> 'a list -> 'a
  val filter : ('a -> bool) -> 'a list -> 'a list
  val find_all : ('a -> bool) -> 'a list -> 'a list
  val partition : ('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 -> ('a * 'b) list -> bool
  val mem_assq : 'a -> ('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 : ('a -> 'a -> int) -> 'a list -> 'a list
  val stable_sort : ('a -> 'a -> int) -> 'a list -> 'a list
end