@article{IM2_1998_62_1_a5,
     author = {O. A. Timoshin},
     title = {The best approximation to the operator of the second mixed derivative},
     journal = {Izvestiya. Mathematics },
     pages = {191--200},
     publisher = {mathdoc},
     volume = {62},
     number = {1},
     year = {1998},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1998_62_1_a5/}
}