`sig val length : 'a list -> int val cons : 'a -> 'a list -> 'a list 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 iteri : (int -> 'a -> unit) -> 'a list -> unit val map : ('a -> 'b) -> 'a list -> 'b list val mapi : (int -> '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 val fast_sort : ('a -> 'a -> int) -> 'a list -> 'a list val sort_uniq : ('a -> 'a -> int) -> 'a list -> 'a list val merge : ('a -> 'a -> int) -> 'a list -> 'a list -> 'a list end`