## Multiple insertion
```
# let insert_mult n x lst =
  if n <= 0 then
    invalid_arg "insert_mult: n must be > 0"
  else
    let rec aux count = function
      | [] -> []
      | e::t ->
          if (count = n) then
            e :: x :: aux 1 t
          else
            e :: aux (count + 1) t
    in
    match lst with
    | [] -> []
    | z::f -> z :: aux 0 f

val insert_mult: int -> 'a -> 'a list -> 'a list = <fun>
```