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The power of commuting with finite sets of words
 In Proc. STACS’05, Springer LNCS 3404
, 2005
"... We construct a finite language L such that the largest language commuting with L is not recursively enumerable. This gives a negative answer to the question raised by Conway in 1971 and also strongly disproves Conway’s conjecture on contextfreeness of maximal solutions of systems of semilinear ine ..."
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We construct a finite language L such that the largest language commuting with L is not recursively enumerable. This gives a negative answer to the question raised by Conway in 1971 and also strongly disproves Conway’s conjecture on contextfreeness of maximal solutions of systems of semilinear inequalities. 1
Simple language equations
 Bull. Eur. Assoc. Theor. Comput. Sci. EATCS
, 2005
"... Abstract. We survey results, both positive and negative, on regularity of maximal solutions of systems of implicit language equations and inequalities. These results concern inequalities with constant righthand sides, onesided linear inequalities, inequalities with restrictions on constants, and c ..."
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Abstract. We survey results, both positive and negative, on regularity of maximal solutions of systems of implicit language equations and inequalities. These results concern inequalities with constant righthand sides, onesided linear inequalities, inequalities with restrictions on constants, and commutation equations and inequalities. In addition, we present some of these results in a generalized form in order to underline common principles. 1.
Simple equations on binary factorial languages
, 2008
"... We consider equations on the monoid of factorial languages on the binary alphabet. We use the notion of a canonical decomposition of a factorial language and previous results by Avgustinovich and the author to solve several simple equations on binary factorial languages including X n = Y n, the comm ..."
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We consider equations on the monoid of factorial languages on the binary alphabet. We use the notion of a canonical decomposition of a factorial language and previous results by Avgustinovich and the author to solve several simple equations on binary factorial languages including X n = Y n, the commutation equation XY = Y X and the conjugacy equation XZ = ZY. At the end of the paper we discuss the difficulties hindering to reduce equations on factorial languages to equations on words and to enlarge the alphabet considered.
Canonical decomposition of a catenation of factorial languages
 Siberian Electronic Mathematical Reports 4 (2007) 14–22
"... Abstract. According to a previous result by S. V. Avgustinovich and the author, each factorial language admits a unique canonical decomposition to a catenation of factorial languages. In this paper, we analyze the appearance of the canonical decomposition of a catenation of two factorial languages w ..."
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Abstract. According to a previous result by S. V. Avgustinovich and the author, each factorial language admits a unique canonical decomposition to a catenation of factorial languages. In this paper, we analyze the appearance of the canonical decomposition of a catenation of two factorial languages whose canonical decompositions are given. 1.