2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/34927Hamiltonian description of gravitational field contained in a spacetime region with boundary $S$ being a null-like hypersurface (a wave front) is discussed. Complete generating formula for the Hamiltonian dynamics (with no surface integrals neglected) is presented. A quasi-local proof of the 1-st law of black holes thermodynamics is obtained as a consequence, in case when $S$ is a non-expanding horizon. The 0-th law and Penrose inequalities are discussed from this point of view.10 pages, to appear in Proceedings of the Seventh Hungarian Relativity WorkshopGeneral Relativity and Quantum Cosmologytext