@article{TM_1974_131_a4,
     author = {V. I. Burenkov},
     title = {The density of infinitely differentiable functions in {Sobolev} spaces for an arbitrary open set},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {39--50},
     publisher = {mathdoc},
     volume = {131},
     year = {1974},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TM_1974_131_a4/}
}