Abstract:
Every computable universal algebra has a finitely presented expansion. On the other hand, there are examples of finitely generated, computably enumerable universal algebras with no finitely presented expansions. It is natural to ask whether such examples can be found in well-known classes of algebras such as groups and semigroups. Here we build an example of a finitely generated, infinite, computably enumerable semigroup with no finitely presented expansions.We also discuss other interesting computability-theoretic properties of this semigroup.
Citation:
D. R. Hirschfeldt, B. Khoussainov, “Finitely presented expansions of computably enumerable semigroups”, Algebra Logika, 51:5 (2012), 652–667; Algebra and Logic, 51:5 (2012), 435–444
Nadim Kasymov, Nadira Karimova, Bakh Khoussainov, Proceedings of the 39th Annual ACM/IEEE Symposium on Logic in Computer Science, 2024, 1
Valentino Delle Rose, Luca San Mauro, Andrea Sorbi, “Classifying word problems of finitely generated algebras via computable reducibility”, Int. J. Algebra Comput., 33:04 (2023), 751
Bakh Khoussainov, Lecture Notes in Computer Science, 10936, Sailing Routes in the World of Computation, 2018, 1
G. Wu, H. Wu, “Degrees of word problem for algebras without finitely presented expansions”, Theory and Applications of Models of Computation, TAMC 2017, Lecture Notes in Computer Science, 10185, eds. T. Gopal, G. Jager, S. Steila, Springler, 2017, 642–652
A. Gavryushkin, B. Khoussainov, F. Stephan, “Reducibilities among equivalence relations induced by recursively enumerable structures”, Theor. Comput. Sci., 612 (2016), 137–152