@article{ZNSL_1974_45_a3,
     author = {Yu. A. Volkov},
     title = {Extentions of {Darboux--Sauer} and {Pogorelov} theorems},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {63--67},
     publisher = {mathdoc},
     volume = {45},
     year = {1974},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1974_45_a3/}
}