@article{CM_1939__6__228_0,
     author = {Kupradze, V.},
     title = {Zur Frage der Ausbreitung elektromagnetischer Wellen in einem inhomogenen ebenen Medium},
     journal = {Compositio Mathematica},
     pages = {228--234},
     publisher = {Johnson Reprint Corporation},
     volume = {6},
     year = {1939},
     zbl = {0021.17803},
     language = {de},
     url = {archive.numdam.org/item/CM_1939__6__228_0/}
}

Kupradze, V. Zur Frage der Ausbreitung elektromagnetischer Wellen in einem inhomogenen ebenen Medium. Compositio Mathematica, Tome 6 (1939) , pp. 228-234. http://archive.numdam.org/item/CM_1939__6__228_0/