function catsChanged(clicked) {
	var targetValue = 0;
	
	$$('.category_value').each(function(checkbox) {
		if(checkbox.checked)
		targetValue |= checkbox.value;
	});
	
	if(targetValue == 0) {
		$$('div .article').each(function(art) { new Effect.Opacity(art, { to: 1, duration: 0.5 }) });
		return;
	}
	
	$$('div .article').each(function(art) {
		var artId    = art.id.split('_')[1];
		var artValue = $F('item_' + artId + '_cat_value');
		
		new Effect.Opacity(art, { to: (((artValue & targetValue) == targetValue) ? 1 : 0.25), duration: 0.5 });
	});
}