a^{a1,a2}_{a0,v0} b^{}_{a3,v1} eta1^{a3}_{a2} a+(a0) a+(v0) a+(v1) a-(a1)
-1/2 a^{a1,a2}_{a0,v0} b^{}_{a3,v1} lambda2^{a0,a3}_{a1,a2} a+(v0) a+(v1)