2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/74782We study extremality properties of covering families of rational curves on projective varieties. Among others, we show that on a normal and Q-factorial projective variety of dimension at most 4, every covering and quasi-unsplit family of rational curves generates a geometric extremal ray of the Mori cone.13 pagesAlgebraic Geometry14E30,14J99,14M99On covering and quasi-unsplit families of rational curvestext