Renormalization-group calculation of the critical exponents for percolation

The relation between the $s$-state Ashkin-Teller-Potts model and the percolation problem given by Kasteleyn and Fortuin is used to formulate a renormalization-group treatment of the percolation problem. The variational renormalization-group scheme given by Kadanoff is used to treat the $s$-state model on a square lattice and the $s\to 1$ limit is taken to get the critical exponents for the percolation problem.