@article{FORUM_1989__1_3_141612,
     author = {Werner Ballmann},
     title = {On the {Dirichlet} {Problem} at {Infinity} for {Manifolds} of {Nonpositive} {Curvature.}},
     journal = {Forum mathematicum},
     pages = {201--214},
     publisher = {mathdoc},
     volume = {1},
     number = {3},
     year = {1989},
     zbl = {0661.53026},
     url = {http://geodesic.mathdoc.fr/item/FORUM_1989__1_3_141612/}
}