Is usually terrible. Possibly because writing is just plain hard, harder in your second language (and scientists are rarely writing in their mother language), and possibly because even highly skilled textbook authors want to create demand for lectures where they explain in person what they obfuscated in books.
I am especially interested in good mathematical style.
- Knuth, D. E., Larrabee, T. L., & Roberts, P. M.(1989). Mathematical Writing. [Washington, D.C.]: Mathematical Association of America. Online.
- Lamport, L. (1995). How to Write a Proof. The American Mathematical Monthly, 102(7), 600–608. DOI. Online.
- Lamport, L. (2012). How to write a 21st century proof. Journal of Fixed Point Theory and Applications, 11(1), 43–63. DOI. Online.