https://www.wiley.com/college/engin/balabanian293512/pdf/ch04.pdf

http://w3.ualg.pt/~jmcardo/ensino/sistdigitais01/BookKatz/chapter03.pdf

https://www.cs.indiana.edu/classes/b441-sjoh/notes/ADD/4.pdf

http://eng.staff.alexu.edu.eg/~mbanna/Logic_Circuit_Design_EE242/EE242_Class_Notes_ logic design.pdf

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