@article{10_1090_S1079_6762_03_00105_7,
     author = {Wise, Daniel},
     title = {Nonpositive immersions, sectional curvature, and subgroup properties},
     journal = {Electronic research announcements of the American Mathematical Society},
     pages = {1--9},
     year = {2003},
     volume = {09},
     doi = {10.1090/S1079-6762-03-00105-7},
     url = {http://geodesic.mathdoc.fr/articles/10.1090/S1079-6762-03-00105-7/}
}