public void undo(Board board) {		
			//Searches desired column from top to bottom
		int h = Util.firstEmptyPosition(board, this.getCol());		
		if (h != board.getHeight()) {
			if (h < Util.ERRORTHRESHOLD) {
				h = Board.MINHEIGHT - 1;
			}
			board.setPosition(this.getCol(), h+1, Counter.EMPTY);
		}
		else {
			System.err.println("Nothing to undo.");
		}
	}