Abstract

In this thesis we study several interconnected decision problems and effective constructions on words and languages, as well as some related problems, all being connected with different orders of words. Most important ones are mentioned in what follows. Decision problems: the slenderness problem for context-free languages, the problem of whether or not a language (regular or context-free) is the set of prefixes (factors, subwords) of an infinite word, the confluence problem with respect to a quasi order. Effective constructions: effective representations of slender context-free languages, effective regularity of the sets of subwords or superwords of a given language. Related problems: the characterization of slender context-free languages, a generalization of Haines' theorem, generalized factor relations and a generalization of Higman's theorem. Keywords: language theory, combinatorics on words, decidability, effective construction, quasi order, slender language, prefix, factor, conflu...

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