Here, I've included personal notes for various physics and mathematics courses, textbooks, and papers I've worked through over the years. All of these notes are not intended as polished works and by no means intended as stand-alone works, but are just compilations of thoughts and some calculations that helped me while I was going through the material in question. Hopefully, it'll serve to help others as well in their struggles.
I've provided the notes here; the references are all provided in the respective subsections. I really hope these help!
(References here.)