@article{MM2_1991__72_1_155641,
     author = {Marc Troynaov},
     title = {The {Schwarz} {Lemma} for nonpositively curved riemannian surfaces.},
     journal = {Manuscripta mathematica},
     pages = {251--256},
     publisher = {mathdoc},
     volume = {72},
     number = {1},
     year = {1991},
     zbl = {0736.53043},
     url = {http://geodesic.mathdoc.fr/item/MM2_1991__72_1_155641/}
}