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Nondeterministic forgetting automata are less powerful than deterministic linear bounded automata. (English) Zbl 0853.68118
Summary: Forgetting automata are nondeterministic linear bounded automata with restricted rewriting capability: any input symbol can only be “erased” (rewritten by a special symbol) or completely “deleted”. They are, in fact, a special case of 2-change automata introduced by B. von Braunmühl and R. Verbeek [Lect. Notes Comput. Sci. 67, 91-100 (1979; Zbl 0404.68081)].
This paper shows by the method of diagonalization that, for any $$k$$, $$k$$-change automata with a fixed (work) alphabet recognize a proper subclass of the class of languages recognizable by deterministic linear bounded automata (i.e. deterministic context-sensitive languages).

##### MSC:
 68Q45 Formal languages and automata
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##### References:
 [1] von Braunmühl B., Verbeek R.: Finite change automata. Proc. of 4th GI Conference on Theoretical Computer Science, Lecture Notes in Computer Science (LNCS) 67, Springer, Berlin (1979), 91-100. · Zbl 0404.68081 [2] Hopcroft J., Ullman J.: Formal languages and their relation to automata. Addison-Wesley, 1969. · Zbl 0196.01701 [3] Jančar P., Mráz F., Plátek M.: Characterization of context-free languages by erasing automata. Proc. of the symp. Mathematical Foundations of Computer Science (MFCS) 1992, Prague, Czechoslovakia, LNCS 629, Springer (1992), 307-314. [4] Jančar P., Mráz F., Plátek M.: A taxonomy of forgetting automata. accepted to MFCS’93, Gdansk, Poland, to appear in LNCS, Springer (1993). · Zbl 0925.68320 [5] Savitch W. J.: Relationships between nondeterministic and deterministic tape complexities. J. of Computer and System Sciences 4 (1970), 177-192. · Zbl 0188.33502 · doi:10.1016/S0022-0000(70)80006-X
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