@article{VMUMM_1990_4_a1,
     author = {V. V. Pospelov},
     title = {Approximation of a function of two variables by the sum of products of functions of one variable in {Sobolev} spaces},
     journal = {Vestnik Moskovskogo universiteta. Matematika, mehanika},
     pages = {6--10},
     publisher = {mathdoc},
     number = {4},
     year = {1990},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VMUMM_1990_4_a1/}
}