2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/38933A general discussion is presented of the response of a gauge-field system to external magnetic fields, in the light of a theorem due to S. Elitzur. As a result a natural understanding emerges of some recent puzzling results from lattice MC simulations, as well as of the phenomenon of ``perfect diamagnetism'' of non-abelian gauge theories, discovered almost ten years ago.3 pages (RevTeX)High Energy Physics - LatticeHigh Energy Physics - Theorytext