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Unformatted text preview: CSCI 2670 Introduction to Theory of Computing September 13, 2005 Announcement • Homework due next Tuesday 9/20 – Use the pumping lemma to prove the following language is not regular • A = {ww R  w ∈ {a,b} * } – 1.54, 2.1 c & d, 2.4 c & e, 2.6 b & d • Note in 2.6 d, it is possible that i = j Agenda • Last week – Proved correspondence between regular languages and regular expressions • This week – Learn how to prove a language is not regular – Introduce a new class of language – Introduce a new type of state machine Nonregular languages • So far, we have explored several ways to identify regular languages – DFA’s, NFA’s, GNFA’s, RE’s • There are many nonregular languages – {0 n 1 n  n ≥ 0} – {101,101001,1010010001,…} – {w  w has the same number of 0s and 1s} • How can we tell if a language is not regular? Property of regular languages • All regular languages can be generated by finite automata • States must be reused if the length of a string is greater than the number of states • If states are reused, there will be repetition The pumping lemma...
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This note was uploaded on 02/07/2011 for the course CS 501 taught by Professor Sm during the Spring '11 term at Indiana.
 Spring '11
 sm

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