Often when I read a chapter in a textbook and don't understand something, I find "reading notes" by other students extremely helpful. Oftentimes in these notes other readers have simply written down summaries of the sections in their own words. These descriptions of the "same thing" in different words helps me fill in the gaps and clarify the things that confused me. As an example, have a look at the notes by Zhong-Zhi Xianyu or the reading notes by Michael Nielsen for John Baez' book "Gauge Fields and Knots". Unfortunately it's not always easy to find good notes. Thus, my question: Do you know any great reading notes? They don't have to be about a complete textbook. Summaries/notes on specific sections would also be great. If yes, please post a link to them here. Notes for popular textbooks like Peskin-Schröder, Jackson, Goldstein, etc. would be awesome. So far, I wasn't able to find any.