1/2 a^{a0,a2}_{c0,c4} b^{c3,c4}_{c1,c2} c^{a1}_{a3} eta1^{a3}_{a2} a+(c0) a+(c1) a+(c2) a-(a1) a-(a0) a-(c3)
+1/8 a^{a0,a1}_{c2,c3} b^{c2,c3}_{c0,c1} c^{a3}_{a2} a+(c0) a+(c1) a+(a2) a-(a3) a-(a1) a-(a0)
+1/4 a^{a0,a2}_{c2,c3} b^{c2,c3}_{c0,c1} c^{a1}_{a3} eta1^{a3}_{a2} a+(c0) a+(c1) a-(a1) a-(a0)