Abstract
Bergstra and Tucker [1, 2] proved that computable universal algebras have finitely presented expansions. Bergstra and Tucker, and Goncharov, independently, asked whether all finitely generated computably enumerable algebras have finitely presented expansions. Khoussainov and Hirschfeldt [3] constructed finitely generated, infinite c.e. semigroups without finitely presented expansions; furthermore, Khoussainov and Miasnikov [6] found such examples in class of groups and algebras over finite fields. In this paper, we consider Turing degrees of the word problem for semigroups constructed in [3] and for algebras over finite fields constructed in [6], and prove that the word problem for such semigroups and algebras appears in all nonzero c.e. degrees respectively.
Both authors are partially supported by MOE2011-T2-1-071 (ARC 17/11, M45110030) from Ministry of Education of Singapore, and by AcRF grants RG29/14, M4011274 from Nanyang Technological University.
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References
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Acknowledgement
G. Wu is partially supported by AcRF grants MOE2016-T2-1-083 from Ministry of Education of Singapore, RG29/14, M4011274 and RG32/16, M4011672 from Nanyang Technological University and Ministry of Education of Singapore.
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Wu, G., Wu, H. (2017). Degrees of Word Problem for Algebras Without Finitely Presented Expansions. In: Gopal, T., Jäger , G., Steila, S. (eds) Theory and Applications of Models of Computation. TAMC 2017. Lecture Notes in Computer Science(), vol 10185. Springer, Cham. https://doi.org/10.1007/978-3-319-55911-7_46
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DOI: https://doi.org/10.1007/978-3-319-55911-7_46
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