@article{ASENS_1991_4_24_5_605_0,
     author = {Bangert, V. and Schroeder, V.},
     title = {Existence of flat tori in analytic manifolds of nonpositive curvature},
     journal = {Annales scientifiques de l'\'Ecole Normale Sup\'erieure},
     pages = {605--634},
     publisher = {Elsevier},
     volume = {Ser. 4, 24},
     number = {5},
     year = {1991},
     doi = {10.24033/asens.1638},
     mrnumber = {92k:53110},
     zbl = {0760.53032},
     language = {en},
     url = {http://www.numdam.org/articles/10.24033/asens.1638/}
}