1/4 a^{v0}_{c2} b^{c0,c1}_{a0,a1} c^{c2}_{v0} a+(a0) a+(a1) a-(c1) a-(c0)
-1/2 a^{v0}_{c2} b^{c0,c2}_{a0,a1} c^{c1}_{v0} a+(a0) a+(a1) a-(c1) a-(c0)