1/2 a^{a1}_{c0,a0} b^{c0}_{a2,a3,v0} a+(a0) a+(a2) a+(a3) a+(v0) a-(a1)
+a^{a2}_{c0,a0} b^{c0}_{a1,a3,v0} eta1^{a3}_{a2} a+(a0) a+(a1) a+(v0)
-a^{a2}_{c0,a0} b^{c1}_{a1,a3,v0} eta1^{a3}_{a2} a+(c0) a+(a0) a+(a1) a+(v0) a-(c1)