1. The algebraic theory of context-free languages;Chomsky,1963
2. Rational sets in commutative monoids
3. On relations defined by generalized finite automata;Elgot;IBM J. Res. Develop.,1965
4. Multitape one-way non-writing automata;Fischer;J. Comput. System Sci.,1968
5. Decision problems of phrase-structure grammars;Landweber;IEEE Trans.,1964