1. Finite state languages;Chomsky;Information and Control,1958
2. Context-free grammars and push-down storage;Chomsky,1962
3. The algebraic theory of context-free language;Chomsky,1962
4. Two families of languages related to Algol;Ginsburg;J. Assoc. Computing Mach.,1961
5. Symmetric random walks on groups;Kesten;Trans. Am. Math. Soc.,1959