2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/60946This paper studies the infinitesimal variation of the Lefschetz decomposition associated with a compatible sl_2-representation on a graded algebra. This allows to prove that the Jordan-Lefschetz property holds infinitesimally for the Kaehler Lie algebra (introduced by Looijenga and Lunts) of any compact Kaehler manifold. As a second application we describe how the space of harmonic forms changes when a Ricci-flat Kaehler form is deformed infinitesimally.Revised version: Lemma in Sect. 3 corrected, typos corrected, Corollary in Sect. 4 addedAlgebraic Geometrytext