@article{MS2_1979__44_166637,
     author = {Gudlaugur Thorbergsson},
     title = {Non-hyperbolic closed geodesics.},
     journal = {Mathematica Scandinavica},
     pages = {135--148},
     publisher = {mathdoc},
     volume = {44},
     year = {1979},
     zbl = {0414.53037},
     url = {http://geodesic.mathdoc.fr/item/MS2_1979__44_166637/}
}