window.addEvent('load', function(){
	$$('#main_list li').each(function(el){
		var a = el.getElement('.a');
		var b = el.getElement('.b');
		b.setStyle('display', 'block');
		el.addEvent('mouseenter', function(){
			a.fade('out');
		});
		el.addEvent('mouseleave', function(){
			a.fade('in');
		});
	});
});