@article{IM_1983__71_143006,
     author = {Werner Ballmann},
     title = {On the {Lengths} of {Closed} {Geodesics} on {Convex} {Surfaces.}},
     journal = {Inventiones mathematicae},
     pages = {593--598},
     year = {1983},
     volume = {71},
     zbl = {0505.53020},
     url = {http://geodesic.mathdoc.fr/item/IM_1983__71_143006/}
}