1/4 a^{a0}_{c2} b^{c0,c1}_{v0,v1} c^{c2}_{a1} eta1^{a1}_{a0} a+(v0) a+(v1) a-(c1) a-(c0)
-1/2 a^{a0}_{c2} b^{c0,c2}_{v0,v1} c^{c1}_{a1} eta1^{a1}_{a0} a+(v0) a+(v1) a-(c1) a-(c0)