@article{10_4171_ggd_72,
     author = {Udo Baumgartner and G\"unter Schlichting and George A. Willis},
     title = {Geometric characterization of flat groups of automorphisms},
     journal = {Groups, geometry, and dynamics},
     pages = {1--13},
     year = {2010},
     volume = {4},
     number = {1},
     doi = {10.4171/ggd/72},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/ggd/72/}
}