function nascondi(id){
       var elem;
        elem = document.getElementById(id);
        if (elem != null)
        {       
            if (elem.style.display == "none")
            {
                elem.style.display = "block";
                return "block";
            }
            else
            {
                elem.style.display = "none";
                return "none";
            }
        }
   
}