function $(idname)
{
    var my_obj = document.getElementById(idname);
    return my_obj;
}
function toggle_nav(obj)
{ 
   if(obj==null)
   {
   }
   else {
	
    for (i = 0; i<= 3; i++  )
    { 
        var sub_nav = $("sub_nav_" + i);      
        if (obj == i)
        {
            sub_nav.style.display = "block";
        }
        else
        {
            sub_nav.style.display = "none";
        }
    }
           
  
	}
}