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