2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/85629We present a general proof based on Kramers-Kronig relations that, in a normal or anomalous dispersive linear medium, any (discontinuitynonanalytic disturbance) in an electromagnetic pulse can not propagate faster than the phase velocity, $c$. Consequently the information carried by the discontinuity (nonanalytical disturbance) can not be transmitted superluminally.3 figuresClassical Physicstext