Given two consecutive prime numbers p1 and p2, the gap between them is p2 p1. For example, the gap between 11 and 13 is 2; the gap between 503 and 509 is 6. For this problem, write a C function unsigned long primeGap(const mpz_t a, const mpz_t b) that finds the largest gap between a pair of consecutive prime numbers in a given interval [a, b]; a and b can be any positive numbers with a < b. You should use GMP, the GNU Multiple Precision Arithmetic Library. C programming.