1. Ash CJ, Knight JF (2000) Computable structures and the hyperarithmetical hierarchy. Elsevier, Amsterdam
2. Chomsky N (1959) On certain formal properties of grammars. Inf Control 2:137–167
3. Cooper SB (2004) Computability theory. Chapman & Hall, Boca Raton
4. Cutland NJ (1997) Computability. An introduction to recursive function theory. Cambridge University Press, Cambridge
5. Davis M (1958) Computability and unsolvability. McGraw-Hill, New York