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