function showCurrentSubMenu(book){
        var subMenu = document.getElementById('sub' + book);
        var activeBookSub = document.getElementById('sub' + currentBookId);
        subMenu.style.display = 'none';
        activeBookSub.style.display = 'inline';
          
        var hoverTab = document.getElementById(book);
        hoverTab.className = menuItemClass;
        var activeBookTab = document.getElementById(currentBookId);
        activeBookTab.className = menuItemActiveClass;
    
}
                    
function switchSubMenu(book){
        var subMenu = document.getElementById('sub' + book);
        var activeBookSub = document.getElementById('sub' + currentBookId);
        activeBookSub.style.display = 'none';
        subMenu.style.display = 'inline';
        
        var activeBookTab = document.getElementById(currentBookId);
        activeBookTab.className = menuItemClass;
        var hoverTab = document.getElementById(book);
        hoverTab.className = menuItemActiveClass;
}


function MM_preloadImages() { //v3.0
  var d=document; if(d.images){ if(!d.MM_p) d.MM_p=new Array();
    var i,j=d.MM_p.length,a=MM_preloadImages.arguments; for(i=0; i<a.length; i++)
    if (a[i].indexOf("#")!=0){ d.MM_p[j]=new Image; d.MM_p[j++].src=a[i];}}
}

function MM_findObj(n, d) { //v4.01
  var p,i,x;  if(!d) d=document; if((p=n.indexOf("?"))>0&&parent.frames.length) {
    d=parent.frames[n.substring(p+1)].document; n=n.substring(0,p);}
  if(!(x=d[n])&&d.all) x=d.all[n]; for (i=0;!x&&i<d.forms.length;i++) x=d.forms[i][n];
  for(i=0;!x&&d.layers&&i<d.layers.length;i++) x=MM_findObj(n,d.layers[i].document);
  if(!x && d.getElementById) x=d.getElementById(n); return x;
}