@article{DE_2004_40_1_a8,
     author = {V. V. Kulyaba and O. M. Penkin},
     title = {Strong {Stratified} {Sets} and the {Friedrichs} {Inequality}},
     journal = {Differencialʹnye uravneni\^a},
     pages = {69--76},
     publisher = {mathdoc},
     volume = {40},
     number = {1},
     year = {2004},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_2004_40_1_a8/}
}