input: Write a python function to simplify a fraction to its lowest terms.
  assert simplify(50, 100) == (1, 2)
  assert simplify(36, 60) == (3, 5)
  assert simplify(8, 12) == (2, 3)
output: def simplify(numerator, denominator):
      def gcd(a, b):
          while b:
              a, b = b, a % b
          return a
  
      common_divisor = gcd(numerator, denominator)
      return numerator // common_divisor, denominator // common_divisor