# hw_03 - Problem Set 3 Spring 10 Due Thursday Feb 18 in...

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Unformatted text preview: Problem Set 3 Spring 10 Due: Thursday Feb 18 in class before the lecture. Please follow the homework format guidelines posted on the class web page: http://www.cs.uiuc.edu/class/sp10/cs373/ 1. [ Category : Comprehension, Points : 20] Give a regular expression for the following languages: (a) Σ = { a,b } : The set of all strings where the second letter from the start and second letter from the end both are a 's (e.g. babaab ). (b) Σ = { a,b } : The set of all strings that have both aa and bb as a (contiguous) substring. (c) Σ = { a,b,c } : The set of all strings, such that between every a and c there's at least one b . Describe the language of each of the following regular expressions in your own words. Please be speci c and try to minimize the amount of mathematical notation you use. (a) Σ = { a,b } . ( ab + ba ) * (b) Σ = { a,b } . (( a * ) b ( a * ) b ( a * )) * b (c) Σ = { a,b,c } . (( + a + aa + aaa )( b + c )) * ( + a + aa + aaa ) 2. Intersect 'em [ Category : Construction, Points...
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hw_03 - Problem Set 3 Spring 10 Due Thursday Feb 18 in...

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