Finite-Dimensional Extensions of Certain Symmetric Operators(1)
Canadian mathematical bulletin, Tome 16 (1973) no. 3, pp. 455-456

Voir la notice de l'article provenant de la source Cambridge University Press

Let H be a Hilbert space with inner product 〈,). A well-known theorem of von Neumann states that, if S is a symmetric operator in H, then S has a selfadjoint extension in H if and only if S has equal deficiency indices. This result was extended by Naimark, who proved that, even if the deficiency indices of S are unequal, there always exists a Hilbert space H1 such that H ⊆ H1 and S has a selfadjoint extension in H1.
Michael, I. M. Finite-Dimensional Extensions of Certain Symmetric Operators(1). Canadian mathematical bulletin, Tome 16 (1973) no. 3, pp. 455-456. doi: 10.4153/CMB-1973-076-6
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