old_contents: def compute_gcd(m, n):
      """Compute the greatest common divisor by Euclid's Algorithm."""
      while m % n != 0:
          old_m = m
          old_n = n
          m = old_n
          n = old_m % old_n
      return n
  
new_contents: def compute_gcd(m, n):
      """Compute the greatest common divisor (GCD) by Euclid's Algorithm."""
      while m % n != 0:
          old_m = m
          old_n = n
          m = old_n
          n = old_m % old_n
      return n
  
subject: Add GCD abbreviation