@article{MZM_2007_82_3_a4,
     author = {E. D. Livshits},
     title = {On $n${-Term} {Approximation} with {Positive} {Coefficients}},
     journal = {Matemati\v{c}eskie zametki},
     pages = {373--382},
     publisher = {mathdoc},
     volume = {82},
     number = {3},
     year = {2007},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_2007_82_3_a4/}
}