Amalgams of inverse semigroups and reversible two-counter machines
نویسندگان
چکیده
We show that the word problem for an amalgam [S1, S2;U,ω1, ω2] of inverse semigroups may be undecidable even if we assume S1 and S2 (and therefore U) to have finite R-classes and ω1, ω2 to be computable functions, interrupting a series of positive decidability results on the subject. This is achieved by encoding into an appropriate amalgam of inverse semigroups 2-counter machines with sufficient universality, and relating the nature of certain Schützenberger graphs to sequences of computations in the machine.
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