2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/57045The more exact upper estimate of the percolation threshold for the {\it site problem} on the quadratic lattice ${\Bbb Z}^2$ have been found on the basis of the cluster decomposition. It is done by the number estimate of cycles on ${\Bbb Z}^2$ which maybe external boundaries of finite clusters9 pages, 1 figureMathematical PhysicsProbability82B43, 60K35text