Pavol Duris

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We define a language L and show that is <underline>cannot</underline> be recognized by any two way deterministic counter machine. It is done by fooling any given such machine; i.e. showing that if it accepts L' @@@@ L, then L'-L @@@@ &fgr;. For this purpose, an argument stronger than the well known crossing sequence argument needs to be introduced. Since L(More)
It is known that k tapes are no better than two tapes for nondeterministic machines. We show here that two tapes are better than one. In fact, we show that two pushdown stores are better than one tape. Also, k tapes are no better than two for nondeterministic reversal-bounded machines. We show here that two tapes are better than one for such machines. In(More)