15-453 Formal Languages, Automata, and Computation
Lecture 7: Nonregular Languages

So far we have seen three characterizations of regular languages: via DFAs, via NFAs and via regular expressions. In this lecture we analyze how to prove that languages are not regular. The central property of regular languages we take advantage of for this purpose is expressed in the pumping lemma.

• Reading: Ch 1.4, pp. 77-83
• Previous lecture: Regular Expressions
• Next lecture: Context-Free Grammars

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Frank Pfenning