a^{a1,a2}_{c0,a0} b^{}_{c1,a3} eta1^{a3}_{a2} a+(c0) a+(c1) a+(a0) a-(a1)
-1/2 a^{a1,a2}_{c0,a0} b^{}_{c1,a3} lambda2^{a0,a3}_{a1,a2} a+(c0) a+(c1)