docs: def largest_factor_relatively_prime( a, b ):
    """Return the largest factor of a relatively prime to b.
    """
  
    while 1:
      d = gcd( a, b )
      if d <= 1: break
      b = d
      while 1:
        q, r = divmod( a, d )
        if r > 0:
          break
        a = q
    return a