@article{IM2_1977_11_6_a3,
     author = {Ya. B. Pesin},
     title = {Geodesic flows on closed {Riemannian} manifolds without focal points},
     journal = {Izvestiya. Mathematics },
     pages = {1195--1228},
     publisher = {mathdoc},
     volume = {11},
     number = {6},
     year = {1977},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1977_11_6_a3/}
}