Primality

Implement the function

val is_prime : int -> bool

so that is_prime n is true if and only if n is prime.

Examples

let _ = assert (not (is_prime 0))
let _ = assert (not (is_prime 1))
let _ = assert (is_prime 2)
let _ = assert (is_prime 37)
let _ = assert (not (is_prime 57))
let _ = assert (is_prime 97)