Abstract
We show that one can 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 context-freeness of maximal solutions of systems of semi-linear inequalities.
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Kunc, M. (2005). The Power of Commuting with Finite Sets of Words. In: Diekert, V., Durand, B. (eds) STACS 2005. STACS 2005. Lecture Notes in Computer Science, vol 3404. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-31856-9_47
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DOI: https://doi.org/10.1007/978-3-540-31856-9_47
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