2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/67498This is the same version that was previously only on my home page. We give a description of geometric realization which makes it evident that it commutes with products. A similar approach is used to treat cyclic sets. Our approach is similar to those of Drinfeld and Grayson.14 pages, xypicCategory TheoryAlgebraic Topologytext