@article{MAN_1986__276_164196,
     author = {Michael T. Anderson},
     title = {On the {Fundamental} {Group} of {Non-Positively} {Curved} {Manifolds.}},
     journal = {Mathematische Annalen},
     pages = {269--278},
     publisher = {mathdoc},
     volume = {276},
     year = {1986},
     zbl = {0608.53037},
     url = {http://geodesic.mathdoc.fr/item/MAN_1986__276_164196/}
}