@article{AA_1998_10_3_a5,
     author = {S. K. Smirnov and V. P. Havin},
     title = {Approximation and extension problems for some classes of vector fields},
     journal = {Algebra i analiz},
     pages = {133--162},
     publisher = {mathdoc},
     volume = {10},
     number = {3},
     year = {1998},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/AA_1998_10_3_a5/}
}