This method translates an internal position in
self.__board to row and column indices.
# - - - S u d o k u S o l v e r . _ _ x T o R o w C o l - - - def __xToRowCol ( self, x ): """Translate board index to row and column indices. [ x is an integer in [0,BOARD_L) -> return (r,c) where r is x's row and c is x's column ] """ return divmod ( x, 9 )