@article{GDZPPN002205831,
title = {Existence of immersed tori in manifolds of nonpositive curvature.},
journal = {Journal f\"ur die reine und angewandte Mathematik},
volume = {390},
year = {1988},
pages = {32-46},
zbl = {0641.53042},
url = {http://dml.mathdoc.fr/item/GDZPPN002205831}
}
Schroeder, Viktor. Existence of immersed tori in manifolds of nonpositive curvature.. Journal für die reine und angewandte Mathematik, Tome 390 (1988) pp. 32-46. http://gdmltest.u-ga.fr/item/GDZPPN002205831/