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@article{MS2_1968__22_166029, author = {Erik Balslev}, title = {Discreteness of the {Spectrum} of a {Second} {Order} {Elliptic} {Differential} {Operator} in {L2} (rn).}, journal = {Mathematica Scandinavica}, pages = {42--50}, publisher = {mathdoc}, volume = {22}, year = {1968}, zbl = {0176.39901}, url = {http://geodesic.mathdoc.fr/item/MS2_1968__22_166029/} }
Erik Balslev. Discreteness of the Spectrum of a Second Order Elliptic Differential Operator in L2 (rn).. Mathematica Scandinavica, Tome 22 (1968), pp. 42-50. http://geodesic.mathdoc.fr/item/MS2_1968__22_166029/