I love this write up, thanks for sharing. This is a very clearly structured overview of most of the basic formalism I remember from undergrad physics. I'll bookmark this as a refresher if I ever decide to do physics again. That said though, I'm not convinced that I would have been able to follow this document if I had not already been familiar with the formalism. Though the assumptions are generally stated, I suspect their implications are not clear to those approaching the subject for the first time.