@article{IM_1971__12_142068,
     author = {J. Tits and A. Borel},
     title = {\'El\'ements unipotents et sous-groupes paraboliques de groupes r\'eductifes. {I.}},
     journal = {Inventiones mathematicae},
     pages = {95--104},
     publisher = {mathdoc},
     volume = {12},
     year = {1971},
     zbl = {0238.20055},
     url = {http://geodesic.mathdoc.fr/item/IM_1971__12_142068/}
}