In order to investigate homomorphisms which preserve left-dense languages,stable languages,pure languages and so on,let h:X*→X*be a homomorphism,and the following results can be obtained:(1)hpreserves left-dense languages if and only if h(X*)is a left-dense language;(2)If h(X)is an infix code,then hpreserves stable languages and left unitary;(3)If hpreserves noncounting languages,then his an injective and h(X)is a pure language;(4)If h(X)is a comma-free code,then hpreserves very pure languages.That is usefu...
【基金】
Supported by National Natural Science Foundation of China(11226038);
Specialized Research Fund of Education Department of Shaanxi Provincial Government(11JK0499)
【更新日期】
2015-11-04
【分类号】
O153
【正文快照】
1 Introduction and preliminariesLet X be a nonempty finite set of letters,which is called an alphabet.Any finite string over Xiscalled aword.The word that contains no letter is called the empty word,denoted by 1.The set of
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