@article{SM_1989_62_2_a4,
     author = {V. I. Ivanov},
     title = {Approximation in $L_p$ by polynomials in the {Walsh} system},
     journal = {Sbornik. Mathematics},
     pages = {385--402},
     year = {1989},
     volume = {62},
     number = {2},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1989_62_2_a4/}
}