References
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- Gruska , J. 1973 . Proc. of Symp. and Summer School Math. Found. Comp. Sci. . The descriptional complexity of context-free languages . 1973 , High Tatras, Czechoslovakia.
- Marcus , S. 1964 . Finite Grammars arid Automata , Bucharest : The Publ. House of the Romanian Academy of Sciences . in Romanian
- Salomaa , A. 1973 . Formal Languages , New York, , London : Academic Press .