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