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