Remarks on generalized Post Correspondence Problem
It is shown that Post Correspondence Problem remains undecidable even in the case where one of the morphisms is fixed. Accordingly the generalized PCP is undecidable even in the case where both of the morphisms are fixed, and, moreover, the cardinality of their domain alphabet is 7. In particular, GPCP(7) is undecidable. On the other hand, GPCP(2) is not only decidable, but, as we show here, its all solutions can be effectively found.
KeywordsWord Problem Solvability Condition Finite Automaton Binary Case Bounded Delay
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