@article{MS2_1954__2_165550,
     author = {GUNNAR EHRLING},
     title = {On a type of eigenvalue problems for certain elliptic differential operators},
     journal = {Mathematica Scandinavica},
     pages = {267--285},
     publisher = {mathdoc},
     volume = {2},
     year = {1954},
     zbl = {0056.32304},
     url = {http://geodesic.mathdoc.fr/item/MS2_1954__2_165550/}
}