-1/2 a^{a0,a1}_{c0,c1} b^{v0}_{c2} c^{c2}_{a2} eta1^{a2}_{a1} a+(c0) a+(c1) a-(v0) a-(a0)
+a^{a0,a1}_{c0,c2} b^{v0}_{c1} c^{c2}_{a2} eta1^{a2}_{a1} a+(c0) a+(c1) a-(v0) a-(a0)