function blocking(nr)
{
 	if (document.layers)
	{
		 current = (document.layers[nr].display == 'none') ? 'block' : 'none';
		 document.layers[nr].display = current;
	}
	else if (document.all)
	{
		 current = (document.all[nr].style.display == 'none') ? 'block' : 'none';
		 document.all[nr].style.display = current;
 	}
 	else if (document.getElementById)
 	{
 		vista = (document.getElementById(nr).style.display == 'none') ? 'block' : 'none';
 		document.getElementById(nr).style.display = vista;
 	}
}