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This paper gives a personal account of some developments in automata theory and computational complexity theory. Though the account is subjective and deals primarily with the research areas of direct interest to the author, it discusses the underlying beliefs and philosophy which guided this research as well as the intellectual environment and the ideas and contacts which influenced it. An attempt...
We define alternating Turing Machines which are like nondeterministic Turing Machines, except that existential and universal quantifiers alternate. Alternation links up time and space complexities rather well, in that alternating polynomial time equals deterministic polynomial space, and alternating linear space equals deterministic exponential time. Such considerations lead to a two-person game complete...
Families of languages recognized by multi-head writing finite automata are considered. For n≥1, an n-head writing finite automaton (n-wfa) is a finite state device with n one-way read-write heads on a single input tape. Relationships between families of languages recognized by n-wfa (Wn) and other models (e.g. n-head nonwriting finite automata, linear-bounded automata, and real-time buffer automata)...
The s-languages are those languages recognized by a particular restricted form of deterministic pushdown automaton, called an s-machine. They are uniquely characterized by that subset of the standard-form grammars in which each rule has the form Z → aY1...Yn, n≥0, and for which the pairs (Z, a) are distinct among the rules. It is shown that the s-languages have the prefix property, and that they include...
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