2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/206703We consider quantum spin chains and their translationally invariant pure states. We prove Haag duality for quasilocal observables localized in semi-infinite intervals when the von Neumann algebras generated by observables localized in these intervals are not type I.Mathematical Physics82Bxxtext