2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/79303We answer a question of Peller by showing that for any c>1 there exists a power-bounded operator T on a Hilbert space with the property that any operator S similar to T satisfies $\sup_n\|S^n\|>c.$9 pagesFunctional Analysis47A65; 42A50text