1/2 a^{a3,v0}_{c1,a0} b^{c0,c1}_{a1,a2} c^{v1}_{a4} eta1^{a4}_{a3} a+(a0) a+(a1) a+(a2) a-(v1) a-(v0) a-(c0)
-a^{a3,v0}_{c1,a0} b^{c0,c1}_{a1,a4} c^{v1}_{a2} eta1^{a4}_{a3} a+(a0) a+(a1) a+(a2) a-(v1) a-(v0) a-(c0)