Write the function primes which takes in a set of integers by reference and returns a set containing only the prime numbers. You have a helper function available called is_prime that returns true if the value passed to it is prime, and false otherwise. That is, if the input set contains

{1,4,6,7,10,13}

The function will return the set {1, 7, 13}. The input set should not be altered.

Assume all libraries needed for your implementation have already been included.

set primes(set &input) {