@article{SM_1997_188_2_a4,
     author = {E. A. Sevast'yanov},
     title = {Haar problem for sign-sensitive approximations},
     journal = {Sbornik. Mathematics},
     pages = {265--297},
     publisher = {mathdoc},
     volume = {188},
     number = {2},
     year = {1997},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1997_188_2_a4/}
}