What is this "L"-shaped symbol $|\underline{n}$, as in $1+x+x^2/|\underline{2}+x^3/|\underline{3}+\cdots$?

Question

I just got a higher algebra book written by Barnard for a couple bucks. But as I was scrolling through, I found two things that did not make sense. Can anybody tell me the meaning of them (the pic is given below) ? What is that 'L' shaped symbol under the numbers and variables and why is there a limit with "nothing approaching nothing" ?

Answer 1

Given the usage in context, it appears to be factorial. The limit notation is implicitly $\displaystyle\lim_{n\to\infty}.$