2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/36418A free system, considered to be a comparison system, allows for the notion of objective existence and inertial frame. Transformations connecting inertial frames are shown to be either Lorentz or generalized Galilei.19 pages, Latex, 1 figure. Gen. Rel. Grav., to be publishedGeneral Relativity and Quantum Cosmologytext