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