@article{ZVMMF_1973_13_5_a20,
     author = {A. A. Belolipetskii},
     title = {Differentiability of the isochronous surfaces in a linear time-optimal problem},
     journal = {\v{Z}urnal vy\v{c}islitelʹnoj matematiki i matemati\v{c}eskoj fiziki},
     pages = {1319--1323},
     publisher = {mathdoc},
     volume = {13},
     number = {5},
     year = {1973},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZVMMF_1973_13_5_a20/}
}