a^{c0,a0}_{c2,v0} b^{c1}_{a1} c^{c2}_{v1} eta1^{a1}_{a0} a+(v0) a+(v1) a-(c1) a-(c0)
-a^{c0,a0}_{c2,v0} b^{c2}_{a1} c^{c1}_{v1} eta1^{a1}_{a0} a+(v0) a+(v1) a-(c1) a-(c0)