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 ...

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 ...