a^{a0}_{v0} b^{c0,a1}_{c1,v1} c^{c1}_{a2} eta1^{a2}_{a1} a+(v0) a+(v1) a-(a0) a-(c0)
-a^{a1}_{v0} b^{c0,a0}_{c1,v1} c^{c1}_{a2} eta1^{a2}_{a1} a+(v0) a+(v1) a-(a0) a-(c0)