2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/99401A four-node network consisting of a negative loop controlling a positive one is studied. It models some of the features of the p53 gene network. Using piecewise linear dynamics with thresholds, the allowed dynamical classes are fully characterized and coded. The biologically relevant situations are identified and conclusions drawn concerning the effectiveness of the p53 network as a tumour inhibitor mechanism.20 pages Latex, 12 figuresMolecular Networkstext