protected void previous()
	{
		ParseNode previous=myParser.getPreviousAnswer();
		addAnswerToList(previous.getDerivation());
		treePanel.setAnswer(previous);
		treePanel.repaint();
		if (previous.getProductions().length>0)
			statusDisplay.setText("Derived current Strings using "+previous.getProductions()[0]+" production");
		else
			statusDisplay.setText("");
		myPreviousCount++;
		
		if (myStepCount==myPreviousCount)
		{
			myPreviousAction.setEnabled(false);
			myStepCount=0;
			myPreviousCount=0;
		}
		stepAction.setEnabled(true);
		progress.setText(null);
	}