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