October 12

October 12 - CSCI 2670 Introduction to Theory of Computing...

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CSCI 2670 Introduction to Theory of Computing October 12, 2005
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October 12, 2005 2 Agenda •Yester day – Enumerators • Equivalence of enumerators and TM’s – Definition of algorithm • Church-Turing thesis – Decidable languages •Today – More on DFA’s and decidability • Tomorrow
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October 12, 2005 3 Decidable languages A language is decidable if some Turing machine decides it –E v e r y s t r i
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October 12, 2005 4 Some decidable languages •A DFA = {<B,w> | B is a DFA that accepts input string w} •A NFA = {<B,w> | B is an NFA that accepts input string w} •A REX = {<R,w> | R is a regular expression that generates string w}
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October 12, 2005 5 Emptiness testing problem Consider the language E DFA = {<A> | A is a DFA and L(A) = } Theorem: E DFA is a decidable language Proof: Consider the following TM, T T = “On input string <A>, where A is a DFA
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October 12 - CSCI 2670 Introduction to Theory of Computing...

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