1. R. Book, Grammars with time functions, Dissertation, Harvard University, 1969. Also appears as Mathematical Linguistics and Automatic Translation, Report No. NSF-23, The Computation Laboratory, Harvard University, 1969.
2. N. Chomsky andM. P. Schützenberger, The algebraic theory of context-free languages,Computer Programming and Formal Systems, North Holland, Amsterdam, 1963.
3. J. Evey, The theory and application of pushdown store machines, Dissertation, Harvard University, 1963. Also appears as Mathematical Linguistics and Automatic Translation, Report No. NSF-10, The Computation Laboratory, Harvard University, 1963.
4. M. Fischer, Private communication.
5. P. C. Fischer, Turing machines with restricted memory access,Information and Control 9 (1966), 364–379.