2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/130444The theorem by Gell-Mann and Low is a cornerstone in QFT and zero-temperature many-body theory. The standard proof is based on Dyson's time-ordered expansion of the propagator; a proof based on exact identities for the time-propagator is here given.5 pagesMathematical PhysicsStrongly Correlated ElectronsHigh Energy Physics - Theorytext