val find_opt : ('a -> 'b option) -> 'a list -> 'b option
val index_of : ?eq:('a -> 'a -> bool) -> 'a -> 'a list -> int
val index_of_opt : ?eq:('a -> 'a -> bool) -> 'a list -> 'a -> int option
val find_opt : ('a -> 'b option) -> 'a list -> 'b option
val index_of : ?eq:('a -> 'a -> bool) -> 'a -> 'a list -> int
val index_of_opt : ?eq:('a -> 'a -> bool) -> 'a list -> 'a -> int option