-a^{a0,a1}_{c0,c3} b^{c2,c3}_{c1,a2} c^{v1}_{v0} eta1^{a2}_{a1} a+(c0) a+(c1) a+(v0) a-(v1) a-(a0) a-(c2)
+1/4 a^{a0,a1}_{c1,c2} b^{c1,c2}_{c0,a2} c^{v1}_{v0} a+(c0) a+(a2) a+(v0) a-(v1) a-(a1) a-(a0)
-1/2 a^{a0,a1}_{c1,c2} b^{c1,c2}_{c0,a2} c^{v1}_{v0} eta1^{a2}_{a1} a+(c0) a+(v0) a-(v1) a-(a0)