1/2 a^{c0}_{c2} b^{c1,a2}_{a0,a1} c^{c2}_{a3} eta1^{a3}_{a2} a+(a0) a+(a1) a-(c1) a-(c0)
-1/2 a^{c0}_{c2} b^{c2,a2}_{a0,a1} c^{c1}_{a3} eta1^{a3}_{a2} a+(a0) a+(a1) a-(c1) a-(c0)