2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/60095Let $X$ be a smooth $n$-dimensional projective variety over an algebraically closed field $k$ such that $K_X$ is not nef. We give a characterization of non nef extremal rays of $X$ of maximal length (i.e of length $n-1$); in the case of $\ch(k) = 0$ we also characterize non nef rays of length $n-2$.9 pagesAlgebraic Geometry14E30;14J40text