Abstract
We deal with languages that are classes of fully invariant congruences on free semigroups of finite rank. The question is posed as to whether a given fully invariant congruence coincides with a syntactic congruence of the language in question. If all classes of a given fully invariant congruence are rational languages, the corresponding variety is then said to be rational. A number of properties of rational varieties is established—in particular, we point to the way in which they are related to finite varieties.
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Translated fromAlgebra i Logika, Vol. 37, No. 4, pp. 478–492, July–August, 1998.
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Sukhanov, E.V., Shur, A.M. A class of formal languages. Algebr Logic 37, 270–277 (1998). https://doi.org/10.1007/BF02671630
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DOI: https://doi.org/10.1007/BF02671630