1/2 a^{c0,v0}_{c1,a0} b^{c1,v2}_{a1,a2} c^{v1}_{v2} a+(a0) a+(a1) a+(a2) a-(v1) a-(v0) a-(c0)
-1/2 a^{c0,v2}_{c1,a0} b^{c1,v0}_{a1,a2} c^{v1}_{v2} a+(a0) a+(a1) a+(a2) a-(v1) a-(v0) a-(c0)