Isn’t it quite common nowadays for lecturers to just type up their lecture notes and make them available online (for free, obviously)? At least that’s what happ

Isn’t it quite common nowadays for lecturers to just type up their lecture notes and make them available online (for free, obviously)? At least that’s what happened at the last two universities I attended, with other lecturers in the same department possibly reusing said notes. A few of such notes even made it to arXiv. Of course, they will still suggest looking at some textbooks, but only on the rare occasion that they don’t want to include a proof or more information in the notes themselves - and then these books are naturally available in the library’s reference holdings.