@article{MZM_1984_36_3_a9,
     author = {O. A. Timoshin},
     title = {Best approximation of the operator of second mixed derivative in the metrics of $L$ and $C$ on the plane},
     journal = {Matemati\v{c}eskie zametki},
     pages = {369--375},
     publisher = {mathdoc},
     volume = {36},
     number = {3},
     year = {1984},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1984_36_3_a9/}
}