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