2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/120230General relativistic kinematics and the cosmological principle alone imply a monotonicity constraint in the Hubble diagram, which we confront to present-day supernova data. We use the running gradient method of statistical inference by Hall & Heckman (2000). We find no significant departure from monotonicity. The method seems well adapted and we recommend its use with future data.5 pages, 3 figuresAstrophysicstext