a^{c1}_{c0} b^{a0}_{c2} c^{c2}_{a1} eta1^{a1}_{a0} a+(c0) a-(c1)
-a^{c0}_{c2} b^{a0}_{c1} c^{c2}_{a1} eta1^{a1}_{a0} a+(c1) a-(c0)