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