@article{JEMS_2015_17_4_a7,
     author = {Amichai Eisenmann},
     title = {Counting arithmetic subgroups and subgroup growth of virtually free groups},
     journal = {Journal of the European Mathematical Society},
     pages = {925--953},
     publisher = {mathdoc},
     volume = {17},
     number = {4},
     year = {2015},
     doi = {10.4171/jems/522},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/jems/522/}
}