On the rank of the intersection of free subgroups in virtually free groups

摘要

We prove an estimate for the rank of the intersection of free subgroups invirtually free groups, which is analogous to the Hanna Neumann inequality forsubgroups in a free group and to the S.V. Ivanov estimate for subgroups in freeproducts of groups. We also prove a more general estimate for the rank of theintersection of free subgroups in the fundamental group of a finite graph ofgroups with finite edge groups.