@article{SM_1967_2_1_a3,
     author = {Yu. A. Brudnyi},
     title = {Criteria for the existence of derivatives in $L^p$},
     journal = {Sbornik. Mathematics},
     pages = {35--55},
     publisher = {mathdoc},
     volume = {2},
     number = {1},
     year = {1967},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1967_2_1_a3/}
}