Garey, Michael R., and David S. Johnson. 1979. Computers and Intractability: A Guide to the Theory of NP-Completeness. Vol. A series of books in the mathematical sciences. New York: W. H. Freeman.
Harry R. Lewis. 1998. Elements of the Theory of Computation. Upper Saddle River, N.J: Prentice-Hall.
Hopcroft, John. E., Rajeev Motwani, and Jeffrey D. Ullman. 2003. Introduction to Automata Theory, Languages, and Computation. Pearson Education.
Rayward-Smith, V. J. 1986. A First Course in Computability. Vol. Computer science texts. Oxford: Blackwell Scientific.
Sipser, Michael. 2013. Introduction to the Theory of Computation. 3rd ed., International ed. Australia: Cengage Learning.