ABSTRACT
Obviously we can’t write down an expansion that is in nitely long, which is why mathematicians have developed a couple of helpful pieces of shorthand. I have used one of these already in the preceding expansion. e term an ∣ xn 〉 shows us how each piece of the expansion has the same form, just with di erent numbers in place (in sequence) instead of the n. e “…” at the end of the expansion is the hint that it should be going on forever.
