2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/35671The Hessling improvement of the Haag, Narnhofer and Stein principle is analysed in the case of a massless scalar field propagating outside of an extremal R-N black hole. It is found that this sort of ``Quantum (Einstein's) Equivalence Principle'' selects only the R-N vacuum as a physically sensible state, i.e., it selects the temperature $T=0$ only.8 pages, standard LaTex, no figuresGeneral Relativity and Quantum CosmologyHigh Energy Physics - Theorytext