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