1/2 a^{a1,a2}_{c0,a0} b^{v0}_{c1} c^{c1}_{v0} a+(c0) a+(a0) a-(a2) a-(a1)
-1/2 a^{a1,a2}_{c1,a0} b^{v0}_{c0} c^{c1}_{v0} a+(c0) a+(a0) a-(a2) a-(a1)