This was a step glossed over in a proof in the convergence of that I can't seem to understand where certain terms are appearing from.
The identity is
I was able to get something similar by dividing s on the left hand side acros the 0th term to the st term but that still leaves the th and st term untouched and with a final term not in the form of the right hand side. It also leaves in the left hand product.
Just to illustrate what I mean I will take the case of
Something tells me I'm making a wrong assumption somewhere or it's something dumb and obvious but I can't seem to get how this will end up in the form on the lhs.
Any help would be appreciated. Thank you for your time.