ZippelGCD rarely fails on some dense input.

[PoslavskySV]

Test case:

@Test
public void testSmallDomain6() throws Exception {
    IntegersZp64 ring = Rings.Zp64(3);
    MultivariatePolynomialZp64
            a = MultivariatePolynomialZp64.parse("1 + a + 5*b + 7*c + d + 11*e + 13*f + g", ring),
            b = MultivariatePolynomialZp64.parse("1 - a + 5*b - 7*c + d - 11*e + 13*f - g", ring),
            g = MultivariatePolynomialZp64.parse("1 + a - 5*b + 7*c - d + 11*e - 13*f + g", ring);

    int exp = 7;
    a = PolynomialMethods.polyPow(a, exp);
    b = PolynomialMethods.polyPow(b, exp);
    g = PolynomialMethods.polyPow(g, exp);

    MultivariatePolynomialZp64 ag = a.clone().multiply(g);
    MultivariatePolynomialZp64 bg = b.clone().multiply(g);

    System.out.println(PolynomialGCD(ag, bg));
}

[PoslavskySV]

EEZ-GCD works fine on this input.