@article{DAN_1989_308_3_a5,
     author = {I. A. Shevchuk},
     title = {On co-approximation of monotone functions},
     journal = {Doklady Akademii Nauk},
     pages = {537--541},
     publisher = {mathdoc},
     volume = {308},
     number = {3},
     year = {1989},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1989_308_3_a5/}
}