The Undecidability of Some Equivalence Problems Concerning NGSM's and Finite Substitutions

@article{Turakainen1997TheUO,
  title={The Undecidability of Some Equivalence Problems Concerning NGSM's and Finite Substitutions},
  author={Paavo Turakainen},
  journal={Theor. Comput. Sci.},
  year={1997},
  volume={174},
  pages={269-274}
}
It is shown to be undecidable whether an c-free finite substitution and a two-state simple E-free ngsm are equivalent on {a, b}*. Consequently, the state-minimization of such ngsm’s and the nonterminal-minimization of linear grammars having two nonterminals are undecidable. Applications to some other decision problems concerning E-free finite substitutions and linear grammars are also given. Finally it is shown that the time-equivalence problem is undecidable for propagating OL systems, i.e… CONTINUE READING
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