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math.FA2026
On the Cotlar-Stein lemma
Michael Hartz, Marcel Scherer
We give a direct proof of the Cotlar-Stein lemma, which does not rely on the power trick.
math.FA2021
Essential spherical isometries
Marcel Scherer
A result due to Williams, Stampfli and Fillmore shows that an essential isometry on a Hilbert space is a compact perturbation of an isometry if and only if ind$(T…