@article{ZNSL_1969_15_a12,
     author = {N. V. Zepelev},
     title = {The shadow zone on the weak boundary of inhomogeneous mediums},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {187--201},
     publisher = {mathdoc},
     volume = {15},
     year = {1969},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1969_15_a12/}
}