On the rank of the intersection of free subgroups in virtually free groups
arXiv:1301.3115
Abstract
We prove an estimate for the rank of the intersection of free subgroups in virtually free groups, which is analogous to the Hanna Neumann inequality for subgroups in a free group and to the S.V. Ivanov estimate for subgroups in free products of groups. We also prove a more general estimate for the rank of the intersection of free subgroups in the fundamental group of a finite graph of groups with finite edge groups.
arXiv comment10 pages; main results strengthened, references updated, proof of Theorem 1 simplified