text: def gcd(a, b):
      """Greatest Common Divisor by Euclid"""
      a = abs(a)
      b = abs(b)
      if a == 0 and b == 0:
          return 1
      if a == 0:
          return b
      if b == 0:
          return a
      if a < b:
          a, b = b, a
      r = 1
      while r:
          r = a % b
          if r:
              a = b
              b = r
      return b
  