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sav08:playground [2010/03/30 20:28] hossein |
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| ====== Playground ====== | ====== Playground ====== | ||
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| ===== Problem 1: Linear Extension ===== | ===== Problem 1: Linear Extension ===== | ||
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| d) Show that $\leq_1$ is a linear extension of $\leq$ if and only if $(A,\leq_1)$ is a total order and the identity function is a monotone function from $(A,\leq)$ to $(A,\leq_1)$. | d) Show that $\leq_1$ is a linear extension of $\leq$ if and only if $(A,\leq_1)$ is a total order and the identity function is a monotone function from $(A,\leq)$ to $(A,\leq_1)$. | ||
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| + | ===== Perl ===== | ||
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| + | * Write a regular expression that matches a pair of <d> and </d> XML tags and the text between them. The text between the tags can include any other tags. | ||
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| + | * The lexical analyzer typically finds the longest matches. Some languages such as Perl have introduced laziness in matching. By adding a question mark to the end of an operator its lazy version is obtained. For example, given an input 'aaaaa', the expression $a*$ will match the entire input. But the lazy version $a*?$ matches the minimum number of possible characters, which is the empty string. Using lazy repetition find a compact representation for the first part. | ||