-1/4 a^{c0,a3}_{c1,a0} b^{v0,v1}_{a1,a2} c^{c1}_{a4} eta1^{a4}_{a3} a+(a0) a+(a1) a+(a2) a-(v1) a-(v0) a-(c0)
+1/2 a^{c0,a3}_{c1,a0} b^{v0,v1}_{a1,a4} c^{c1}_{a2} eta1^{a4}_{a3} a+(a0) a+(a1) a+(a2) a-(v1) a-(v0) a-(c0)