function fetch_object(idname)
{
    var my_obj = document.getElementById(idname);
    return my_obj;
}
function toggle_nav(obj)
{
    for (i = 0; i<= 8; i++  )
    {  
        var nav_img = fetch_object("nav_" + i);
        var sub_nav = fetch_object("sub_nav_" + i);
        var sub_nav_index =  fetch_object("sub_nav_" + i);
        sub_nav_index.style.display = "none";
        if (obj == i)
        {
            nav_img.className = "navs";
            sub_nav.style.display = "block";
}
        else
        {
            nav_img.className = "navsa";
            sub_nav.style.display = "none";
        }
    }
}