z7a−1 + z7a−3 + 4z6a−2 + 2z6a−4 + 2z6 + az5−z5a−1 + 2z5a−5−12z4a−2−3z4a−4 + 2z4a−6−7z4−3az3−3z3a−1−2z3a−3−z3a−5 + z3a−7 + 12z2a−2 + 4z2a−4−2z2a−6 + 6z2 + az + 2za−1 + 2za−3−za−7−4a−2−2a−4−1