1. Context-Free Grammars and Pushdown Storage;Chomsky,1962
2. Introduction to Formal Language Theory;Harrison,1978
3. Introduction to Automata Theory, Languages, and Computation;Hopcroft,2007
4. Formal Languages and Their Relation to Automata;Hopcroft,1969
5. On context-free languages and pushdown automata;Schützenberger;Inf. Control,1963