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