If a have ln Z[J] = ∫ J²f(t)dt+ a∫ J³dt + b∫ J^4dt, where J=J(t), and I would like to get the 3-point and 4-point functions, how do I proceed? I have tried to use the regular formula for the n-point function, when you derive Z[J] n times in relation to J(t_1)...J(t_n) and after applies J=0, but it doesn't make sense for me, since all the n-point functions will be zero. Actually, I think this particular Z[J] pretty strange because its integrals are not linear in J(t) as I used to see. So, could someone give me a hint? Thanks!