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