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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 DFAs, NFAs, GNFAs, REs 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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 Spring '11
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