@article{SM_2001_192_4_a1,
     author = {J. Verdera and M. S. Mel'nikov and P. V. Paramonov},
     title = {$C^1$-approximation and extension of subharmonic functions},
     journal = {Sbornik. Mathematics},
     pages = {515--535},
     publisher = {mathdoc},
     volume = {192},
     number = {4},
     year = {2001},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_2001_192_4_a1/}
}