@article{10_4171_ggd_638,
     author = {Simon Andr\'e},
     title = {Elementary subgroups of virtually free groups},
     journal = {Groups, geometry, and dynamics},
     pages = {1523--1552},
     year = {2021},
     volume = {15},
     number = {4},
     doi = {10.4171/ggd/638},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/ggd/638/}
}