Fundamental groups of small simplicial complexes

Abstract

The number of nonisomorphic simplicial complexes with up to $n$ vertices increases super-exponentially with $n$, which makes exhaustive computation of invariants associated with such complexes a daunting task. In this paper we provide a complete list of groups that arise as fundamental groups of simplicial complexes with at most $8$ vertices. In addition we give many examples of fundamental groups of complexes with $9$ vertices although the complete classification seems to be beyond reach at the moment. Our results lead to many applications, including progress on the Björner-Lutz conjecture regarding vertex-minimal triangulations of the Poincaré homology sphere, improved recognition criteria for PL triangulations of manifolds and computation of the Karoubi-Weibel invariant for many groups.

26 pages, 4 figures; code available at https://github.com/Lukasz-P-Michalak/FundGroups8complexes and https://github.com/DejanGovc/8cplxs data available at https://doi.org/10.34808/ck4d-ry06