@article{SM_1967_2_3_a2,
     author = {M. Sh. Birman and M. Z. Solomyak},
     title = {Piecewise-polynomial approximations of functions of the classes $W_p^\alpha$},
     journal = {Sbornik. Mathematics},
     pages = {295--317},
     year = {1967},
     volume = {2},
     number = {3},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1967_2_3_a2/}
}