@article{IM2_2016_80_3_a5,
     author = {V. A. Klyachin},
     title = {Modified {Delaunay} empty sphere condition in the problem of approximation of the gradient},
     journal = {Izvestiya. Mathematics},
     pages = {549--556},
     year = {2016},
     volume = {80},
     number = {3},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_2016_80_3_a5/}
}