2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/116381We consider the problem of finding 4 rational squares, such that the product of any two plus the sum of the same two always gives a square. We give some historical background and exhibit one such quadruple.Number TheoryGeneral Mathematics01A45, 11D25, 11G05, 11Y50text