https://docplayer.net/24658933-Chapter-5-synchronous-sequential-logic-5-1-sequential-circuits.html

https://nscpolteksby.ac.id/ebook/files/Ebook/Computer Engineering/Digital Design/Chapter 9 - Asynchronous Sequential Logic.pdf

http://web.ist.utl.pt/luis.tarrataca/classes/computer_architecture/Chapter11-DigitalLogic.pdf