2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/36629Undulatory field functions represent a real wave only if there exists a class of infinite reference systems for which an identical wave is described by the same functional forms.6 pages, PDF from MS-Word97, submitted to Il Nuovo Cimento, Section BGeneral Relativity and Quantum CosmologyAstrophysicstext