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  publisher = {Springer Wien},
  year = {1973},
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  pages = {462--474}
}

@article{Wilke1996,
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  note = {Twentieth International Colloquium on Automata, Languages and Programming}
}

@article{Williams1973,
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  title = {Classification of subshifts of finite type},
  journal = {Annals of Mathematics},
  year = {1973},
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}

@book{RozenbergSalomaa1997,,
  title = {Handbook of Formal Languages, vol. 3: Beyond Words},
  publisher = {Springer-Verlag New York, Inc.},
  year = {1997}
}