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