Revision of upper estimate of percolation threshold on square lattice
  The 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 clusters 
Yu.P. Virchenko, Yu.A. Tolmacheva