@article{SM_1979_35_6_a4,
     author = {K. I. Oskolkov},
     title = {Polygonal approximation of functions of two variables},
     journal = {Sbornik. Mathematics},
     pages = {851--861},
     year = {1979},
     volume = {35},
     number = {6},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1979_35_6_a4/}
}