def __step6(self):
        """
        Add the value found in Step 4 to every element of each covered
        row, and subtract it from every element of each uncovered column.
        Return to Step 4 without altering any stars, primes, or covered
        lines.
        """
        minval = self.__find_smallest()
        for i in range(self.n):
            for j in range(self.n):
                if self.row_covered[i]:
                    self.C[i][j] += minval
                if not self.col_covered[j]:
                    self.C[i][j] -= minval
        return 4
def __step6 ( self ) : minval = self . __find_smallest ( ) for i in range ( self . n ) : for j in range ( self . n ) : if self . row_covered [ i ] : self . C [ i ] [ j ] += minval if not self . col_covered [ j ] : self . C [ i ] [ j ] -= minval return 4
Add the value found in Step 4 to every element of each covered
        row, and subtract it from every element of each uncovered column.
        Return to Step 4 without altering any stars, primes, or covered
        lines.