Some Variations on the Notion of Locally Testable Language
نویسنده
چکیده
The aim of this paper is to complete the characterization of the languages that are Boolean combinations (of a subset) of languages of the form wA∗, A∗w or L(w, r, t, n), where A is an alphabet, w ∈ A, r, t ≥ 0, n ≥ 1 and L(w, r, t, n) denotes the set of all words u in A such that the number of occurrences of the factor w in u is congruent to r threshold t mod n. For each class C of languages such that A+C is a Boolean algebra generated by some of the following types of languages: wA∗, A∗w, A∗wA∗ = L(w, 1, 1, 1) or L(w, r, t, 1), and such that C does not constitute a variety of languages, we compute the smallest variety of languages containing C and the largest variety of languages contained in C.
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