'Greatest common divisor of monomials.'

def gcd(self, other):

    if isinstance(other, Monomial):
        exponents = other.exponents
    elif isinstance(other, (tuple, Tuple)):
        exponents = other
    else:
        raise TypeError(('an    instance    of    Monomial    class    expected,    got    %s' % other))
    return self.rebuild(monomial_gcd(self.exponents, exponents))
