@article{10_1007_s10492_006_0019_5,
     author = {Doktor, Pavel and \v{Z}en{\'\i}\v{s}ek, Alexander},
     title = {The density of infinitely differentiable functions in {Sobolev} spaces with mixed boundary conditions},
     journal = {Applications of Mathematics},
     pages = {517--547},
     publisher = {mathdoc},
     volume = {51},
     number = {5},
     year = {2006},
     doi = {10.1007/s10492-006-0019-5},
     mrnumber = {2261637},
     zbl = {1164.46322},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.1007/s10492-006-0019-5/}
}