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CONTEXT-FREENESS OF THE LANGUAGES OF SCH UTZENBERGER AUTOMATA OF HNN-EXTENSIONS OF FINITE INVERSE SEMIGROUPS
(PUBLICATIONS DE L'INSTITUT MATHEMATIQUE, 2016)
We prove that the Schutzenberger graph of any element of the HNN-extension of a fnite inverse semigroup S with respect to its standard presentation is a context-free graph, showing that the language L recognized by this ...
Undecidability of the word problem for Yamamura’s HNN-extension under nice conditions
(Semigroup Forum, 2016-04)
The solvability of the word problem for Yamamura’s HNN-extensions [S; A1, A2; ϕ] has been proved in some particular cases. However, we show that, contrary to the group case, the word problem for [S; A1A2; ϕ] is undecidable ...