private void verifyPlayersInBoard() throws Exception {
		for (int row = 0; row < _board.length; ++row) {
			for (int col = 0; col < _board.length; ++col) {
				if (isCellEmpty(row, col)) {					
					continue;
				}

				if (_board[row][col] != _leftPlayer && _board[row][col] != _rightPlayer) {
					throw new JProblemsException("Invalid board - Contains invalid player symbol.");
				}
			}
		}
	}