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The nature of the spectrum of a selfadjoint extension of the Laplace operator in a bounded region (fundamental systems of functions with an arbitrary preassigned subsequence of fundamental numbers). (English. Russian original) Zbl 0209.41302

Sov. Math., Dokl. 11, 339-342 (1970); translation from Dokl. Akad. Nauk SSSR 191, 267-269 (1970).

MSC:

35P05 General topics in linear spectral theory for PDEs
35J05 Laplace operator, Helmholtz equation (reduced wave equation), Poisson equation
47A20 Dilations, extensions, compressions of linear operators
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