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