2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/199350A recently proposed theory of modified gravity with an explicit ``anomalous'' coupling of the Ricci curvature to matter is discussed, and an inequality is derived which expresses a necessary and sufficient condition to avoid the notorius Dolgov-Kawasaki instability.4 latex pages, to appear in Phys. Rev. DGeneral Relativity and Quantum Cosmologytext