function switchcolumn (columnname) {
 document.getElementById('contentvolume0').style.display = 'none';
 document.getElementById('contentvolume1').style.display = 'none';
 document.getElementById('contentvolume2').style.display = 'none';
 document.getElementById('contentvolume3').style.display = 'none';
 document.getElementById('contentvolume4').style.display = 'none';
 document.getElementById('contentvolume5').style.display = 'none';
 document.getElementById('contentvolume6').style.display = 'none';
 document.getElementById('contentvolume7').style.display = 'none';
 document.getElementById('contentvolume8').style.display = 'none';   
 document.getElementById('contentvolume9').style.display = 'none';
 document.getElementById('contentvolume10').style.display = 'none';
 document.getElementById('contentvolume11').style.display = 'none';
 document.getElementById('contentvolume12').style.display = 'none';  
 document.getElementById('content'+columnname).style.display = 'block';
}
var lastSelectedMenuItem = null;
function changeSelectedMenuItem(menuItem) {
    if (lastSelectedMenuItem == menuItem) {
        return;
    }
    if (lastSelectedMenuItem == null) {
        lastSelectedMenuItem = document.getElementById("linkvolume0");
    } 
    menuItem.className = "selected";
    lastSelectedMenuItem.className = "";
    lastSelectedMenuItem = menuItem;
}

//-->