function showmenu(val){
   for (i=0; i<4; i++) {
     var tb = document.getElementById('mnu_' + i);
     if (i != val) tb.style.display = "none";
     else tb.style.display = "block";
   }
 }

 function offmenu(val){
   for (i=0; i<4; i++) {
     var tb = document.getElementById('mnu_' + i);
	 tb.style.display = "none";
   }
 }