Restarting automata

Abstract

Motivated by (natural as well as formal) language analysis, we introduce a special kind of the linear bounded automaton - so called restarting automaton (R-automaton). Its computation proceeds in certain cycles; in each cycle, a (bounded) subsequenee of the input word is removed and the computation restarts on the arising shorter word. We consider both nondeterministic and deterministic versions and introduce a natural property of monotonocity. The main result illustrating usefulness of the introduced notions is an elegant characterization of deterministic context-free languages - by deterministic monotonic R-automata. We also show that the monotonocity property is decidable and complete the paper with some related results.