2008/08/13 by Mark Brittenham, Brittenham, Mark, Stuart Margolis +3
Mathematics · Computer Science · #Advanced Topology and Set Theory #semigroups and automata theory #Mathematical Dynamics and Fractals
paper · pdf · doi:10.48550/arxiv.0808.1827
We use topological methods to study the maximal subgroups of the free idempotent generated semigroup on a biordered set. We use these to give an example of a free idempotent generated semigroup with maximal subgroup isomorphic to the free abelian group of rank 2. This is the first example of a non-free subgroup of a free idempotent generated semigroup.