Grushko-like theorems for a class of finitely presented semigroups

Ann Yasuhara
1974 Proceedings of the American Mathematical Society  
An analogue of Grushko's theorem and the unsolvability of the isomorphism problem hold for semigroups in the class of all finitely presented semigroups that have a presentation in which there is no defining relation of the form loA ; this class is not recursive but is recursively enumerable.
doi:10.1090/s0002-9939-1974-0335665-0 fatcat:2yvfoza25nattga4k6u6cfjs5y