Subsemigroups of virtually free groups: finite Malcev presentations and testing for freeness
Alan J. Cain, Edmund F. Robertson, Nik Ruškuc · Mathematical Proceedings of the Cambridge Philosophical Society · 2006
This paper shows that, given a finite subset has a finite Malcev presentation (a type of semigroup presentation which can be used to define any semigroup that embeds in a group), and that such a presentation can be effectively found from any finite generating set.