@article{DAN_1969_189_6_a7,
     author = {Yu. E. Murakhver},
     title = {The velocity of a wave front},
     journal = {Doklady Akademii Nauk},
     pages = {1193--1196},
     publisher = {mathdoc},
     volume = {189},
     number = {6},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1969_189_6_a7/}
}