@article{JLT_2008_18_3_JLT_2008_18_3_a1,
     author = {M. Jotz and K.-H. Neeb },
     title = {Closedness of the {Tangent} {Spaces} to the {Orbits} of {Proper} {Actions}},
     journal = {Journal of Lie theory},
     pages = {517--521},
     publisher = {mathdoc},
     volume = {18},
     number = {3},
     year = {2008},
     url = {http://geodesic.mathdoc.fr/item/JLT_2008_18_3_JLT_2008_18_3_a1/}
}