Angular Momentum in Quantum Mechanics

here is a article i came across while studying angular momentum in quantum mechanics. i found this to be quite useful, some of my earlier doubts(not related to angular momentum) were cleared... although there are a few typos which i could figure out, but i didn't find a way to contact the author, so i can't do much about it.

here's the link:
Angular Momentum Quantum Mechanics for the Rest of Us