−z3a13 + 2za13−z4a12 + z2a12−z5a11 + z3a11−za11−z6a10 + 2z4a10−3z2a10−z7a9 + 4z5a9−8z3a9 + 5za9−a9z−1−2z6a8 + 6z4a8−5z2a8 + a8−z7a7 + 4z5a7−6z3a7 + 5za7−a7z−1−z6a6 + 3z4a6−z2a6−z5a5 + 4z3a5−3za5