I'm very sure this is wrong. I think the f^i(x) should be changed to a g^i(x) where g^i(x) is some function (I'm guessing either Gamma or Beta) and that the infinity sign should be changed to a i-->k where k is some arbitrary value. Reason being f^i(x) will always equal zero and j/i! will also always tend to zero. Besides that I have absolutely nothing to say about this so I was hoping for some expert opinion and perhaps if you could recommend any reading I could do to better my understanding on the subject. Thank you!