@article{TM_1987_180_a76,
     author = {V. V. Kovtunets},
     title = {Differential properties of an operator of best approximation of complex-valued functions},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {135--136},
     year = {1987},
     volume = {180},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TM_1987_180_a76/}
}