program Nqueens (f[]);

begin 
  n = 8; 
  some k; k = 0; 
  do n times 
  begin 
    k >> k0 = k0 + 1; 
    find r in [1 .. n] with 
    begin
      r = f[k];
      donot find i in [1 .. k-1] with 
        either f[i] = r
        orelse either f[i] = r + (k - i)
        orelse f[i] = r - (k - i)
     end
  end
end