function xSwitch(e) { 
	ele=xGetElementById(e);
	if (ele.style.display=='none') {
		xDisplay(e,'block');
		var i = 0;
		while (i<=20) {
			abs = 'abstract_' + i;
			if((test=xGetElementById(abs))) {
				if(abs!=e) xDisplay(abs,'none');
			}
			i++;
		}	
	}
	else if (ele.style.display=='block') xDisplay(e,'none');
}