-1/2 a^{a0}_{c3} b^{c0,c1}_{a1,v0} c^{c3}_{c2} eta1^{a1}_{a0} a+(c2) a+(v0) a-(c1) a-(c0)
+a^{a0}_{c3} b^{c0,c3}_{a1,v0} c^{c2}_{c1} eta1^{a1}_{a0} a+(c1) a+(v0) a-(c2) a-(c0)