## An inverse spectral result for the Neumann operator on planar domains.(English)Zbl 0813.47003

The paper is about the Neumann operator, i.e. the operator transforming the Dirichlet condition to the Neumann condition for the Laplace equation. The author studies the spectrum of this operator and obtains the characterization of the unit disk.

### MSC:

 47A10 Spectrum, resolvent
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