2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/191796The generalized second law of thermodynamics for a system containing a black hole dynamical horizon is proposed in a covariant way. Its validity is also tested in case of adiabatically collapsing thick light shells.JHEP style, 8 pages, 2 figures, version to appear in JHEP with typos correctedGeneral Relativity and Quantum CosmologyAstrophysicsHigh Energy Physics - Theorytext