2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/218924In this paper, a class of combinatorial identities is proved. A method is used which is based on the following rule: counting elements of a given set in two ways and making equal the obtained results. This rule is known as "counting in two ways". The principle of inclusion and exclusion is used for obtaining a class of (0,1)-matrices.5 pagesDiscrete MathematicsG.2.1text