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