function ShowHideNav(tab){
  if (tab == 'tab1') {
        document.getElementById('tab1').style.display = 'block' ;
        document.getElementById('tab2').style.display = 'none' ;
    } else {
        document.getElementById('tab2').style.display = 'block' ;
        document.getElementById('tab1').style.display = 'none' ;
    }
}

function createCookie(name,value,days){
    if (days) {
        var date = new Date();
        date.setTime(date.getTime()+(days*24*60*60*1000));
        var expires = "; expires="+date.toGMTString();
    }
    else var expires = "";
    document.cookie = name+"="+value+expires+"; path=/";
}

function getCookieVal(offset){
    var endstr=document.cookie.indexOf (";", offset);
    if (endstr==-1) endstr=document.cookie.length;
    return unescape(document.cookie.substring(offset, endstr)); 
}

function ReadCookie(name){
    var arg=name+"=";
    var alen=arg.length;
    var clen=document.cookie.length;
    var i=0;
    while (i<clen)
    {
        var j=i+alen;
        if (document.cookie.substring(i, j)==arg) return getCookieVal(j);
        i=document.cookie.indexOf(" ",i)+1;
        if (i==0) break;
    }
    return null; 
}               

function CheckTopNav(){
    if (ReadCookie('topNav') == 'category'){
        ShowHideNav('tab2');
    } else {
        ShowHideNav('tab1');
    }
}