@article{UZKU_1969_129_3_a1,
     author = {A. R. Abdulgamidov},
     title = {Approximation of functions of two variables with respect to {a~Haar} system},
     journal = {U\v{c}\"enye zapiski Kazanskogo universiteta. Seri\^a Fiziko-matemati\v{c}eskie nauki},
     pages = {30--52},
     publisher = {mathdoc},
     volume = {129},
     number = {3},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/UZKU_1969_129_3_a1/}
}