@article{CMH_1983__58_139948,
     author = {W. Ballmann and G. Thorbergsson},
     title = {Some existence theorems for closed geodesics.},
     journal = {Commentarii mathematici Helvetici},
     pages = {416--432},
     publisher = {mathdoc},
     volume = {58},
     year = {1983},
     zbl = {0532.53034},
     url = {http://geodesic.mathdoc.fr/item/CMH_1983__58_139948/}
}