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Title: On Two Letters versus Three
Authors: Kozen, Dexter
Keywords: computer science
technical report
Issue Date: 4-Feb-2002
Publisher: Cornell University
Abstract: If A is a context-free language over a two-letter alphabet, then the set of all words obtained by sorting words in A and the set of all permutations of words in A are context-free. This is false over alphabets of three or more letters. Thus these problems illustrate a difference in behavior between two- and three-letter alphabets.
Appears in Collections:Computer Science Technical Reports

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