1. Indexed grammars—an extension of context free grammars;Aho;J A C M,1968
2. Formal definition of programming languages;Bakker,1967
3. One way stack automata;Ginsburg;JACM,1967
4. Semantics of context-free languages;Knuth;Mathematical Systems Theory,1968
5. Programmed grammars and classes of formal languages;Rosenkrantz;JACM,1969