@article{IM2_1973_7_1_a8,
     author = {V. F. Lazutkin},
     title = {The existence of caustics for a~billiard problem in a~convex domain},
     journal = {Izvestiya. Mathematics},
     pages = {185--214},
     year = {1973},
     volume = {7},
     number = {1},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1973_7_1_a8/}
}