@article{DAN_1985_285_2_a5,
     author = {\'E. V. Nikol'skii},
     title = {The dynamic {Fermat} and {Huygens} principles for a second-order scalar three-dimensional equation of general type},
     journal = {Doklady Akademii Nauk},
     pages = {284--289},
     publisher = {mathdoc},
     volume = {285},
     number = {2},
     year = {1985},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1985_285_2_a5/}
}