1. On the notion of ‘rule of grammar’;Chomsky,1961
2. Bracketed context-free languages
3. J. Doner. Decision Problems of Second-order Logic, (unpublished).
4. Generalized finite automata theory with an application to a decision problem of second-order logic;Thatcher;IBM Res. Rept. RC 1713,1966
5. A further generalization of finite automata;Thatcher;IBM Res. Rept. RC 1846,1967