Summary
In general it is undecidable whether or not the monoid described by a given finite presentation is a free monoid or a group. However, these two decision problems are reducible to a very restricted form of the uniform word problem. So whenever a class of presentations is considered for which this restricted form of the uniform word problem is decidable, then the above decision problems become decidable. This holds in particular for the class of all presentations involving finite string-rewriting systems that are noetherian and confluent.
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References
Book, R.V.: When is a monoid a group? The Church-Rosser case is tractable. Theor. Comput. Sci. 18, 325–331 (1982)
Book, R.V.: Decidable sentences of Church-Rosser congruences. Theor. Comput. Sci. 24, 301–312 (1983)
Book, R.V.: Thue systems as rewriting systems. In: Rewriting techniques and applications. (J.P. Jouannaud, ed). Lect. Notes Comput. Sci. 202, pp. 63–94. Berlin, Heidelberg, New York: Springer 1985
Lallement, G.: Semigroups and combinatorial applications. New York, Chichester, Brisbane, Toronto: John Wiley 1979
Magnus, W., Karrass, A., Solitar, D.: Combinatorial group theory, 2nd. rev. ed., New York: Dover 1976
Markov, A.A.: Impossibility of algorithms for recognizing some properties of associative systems. Dokl. Akad. Nauk SSSR 77, 953–956 (1951)
Mostowski, A.: (Review of Reference 6) J. Symb. Logic 17, 151–152 (1952)
Narendran, P., Otto, F.: Complexity results on the conjugacy problem for monoids. Theor. Comput. Sci. 35, 227–243 (1985)
Otto, F.: Some undecidability results for non-monadic Church-Rosser Thue systems. Theor. Comput. Sci. 33, 261–278 (1984)
Otto, F.: Church-Rosser Thue systems that present free monoids. SIAM J. Comput. (To appear)
Tietze, H.: Über die topologischen Invarianten mehrdimensionaler Mannigfaltigkeiten. Monatsh. Math. Phys. 19, 1–118 (1908)
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Otto, F. On deciding whether a monoid is a free monoid or is a group. Acta Informatica 23, 99–110 (1986). https://doi.org/10.1007/BF00268077
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DOI: https://doi.org/10.1007/BF00268077