2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/155077Given a II$_1$ factor M and a masa A of M, we prove a version of the Schur-Horn Theorem, together with a contractive version. These results are inspired on a recent conjecture of Arveson and Kadison (math.OA/0508482).Major revision. To appear in Indiana Univ. J. of MathOperator AlgebrasFunctional Analysis46L10text