@article{10_4171_ggd_96,
     author = {Mark F. Hagen and Daniel T. Wise},
     title = {Special groups with an elementary hierarchy are virtually free-by-$\ensuremath{\mathbb{Z}}$},
     journal = {Groups, geometry, and dynamics},
     pages = {597--603},
     year = {2010},
     volume = {4},
     number = {3},
     doi = {10.4171/ggd/96},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/ggd/96/}
}