ON THE RIESZ IDEMPOTENT FOR A CLASS OF OPERATORS

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A result from Stampili says that, for hyponormal operators on Hubert space, the Riesz idempotent at an isolated point of a spectrum is self-adjoint, with its range given by null space of both the operator and its adjoint. In this note, we extend this result to operators that are algebraically class H(q). The arguments involve local spectral theory and extensions of a-Browder's theorem.