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@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/} }
GUNNAR EHRLING. On a type of eigenvalue problems for certain elliptic differential operators. Mathematica Scandinavica, Tome 2 (1954), pp. 267-285. http://geodesic.mathdoc.fr/item/MS2_1954__2_165550/