Sur les opérateurs nilpotents d'ordre deux
Spectra of the difference, sum and product of idempotents
We give a simple proof of the relation between the spectra of the difference and product of any two idempotents in a Banach algebra. We also give the relation between the spectra of their sum and product.
A lower bound of the norm of the operator X → AXB + BXA.
Norm of a derivation and hyponormal operators.
Generalized Derivations and Norm Equality in Normed Ideals
2000 Mathematics Subject Classification: 47A10, 47A12, 47A30, 47B10, 47B20, 47B37, 47B47, 47D50. We compare the norm of a generalized derivation on a Hilbert space with the norm of its restrictions to Schatten norm ideals.
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