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NFA, DFA, and regular expressions - 204213 Theory of Computation

NFA, DFA, and regular expressions - 204213 Theory of Computation

NFA, DFA, and regular expressions - 204213 Theory of Computation

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Outline Review Nondeterminism Eq. <strong>of</strong> <strong>NFA</strong>s <strong>and</strong> <strong>DFA</strong>s Closure Reg.Ex. Eq. between Reg.Ex. <strong>and</strong> FAaWhat about other operations?We prove Theorem 1 by simulating two finite automata withone finite automaton.This approach cannot be used directly to prove that the set <strong>of</strong><strong>regular</strong> languages is closed under concatenation. Why?For string w ∈ A 1 ◦ A 2 , there exists a pair x <strong>and</strong> y such thatw = xy <strong>and</strong> x ∈ A 1 <strong>and</strong> y ∈ A 2 .To construct a finite automaton M for A 1 ◦ A 2 from M 1 <strong>and</strong>M 2 that recognize A 1 <strong>and</strong> A 2 we need to simulate M 1 to theend <strong>of</strong> x <strong>and</strong> start simulating M 2 right after that. And it ishard to “tell” where x ends.

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