I’ve written some introductory material that is more approachable than similar writeups. I’d appreciate any comments if you spot any errors or have suggestions on how to improve it. For now it is in simple HTML so it is not very pretty. Eventually I’ll reformat it with LaTex. Papers tend to use different names for these terms. I don’t now if we’ll ever establish a common set of names. I just used names that seem to make sense for this explanation.
The first section is simply the algebraic expansion. The second section places bounds on the Sum. I haven’t seen that done elsewhere so that section may be more interesting.