var current_submenu = '';

function show_submenu (nr) {
   var objId = 'submenu'+nr;
   var obj = document.getElementById(objId);
   obj.style.display = "block";
   
   if (current_submenu != '') {
      objId = 'submenu'+current_submenu;
      obj = document.getElementById(objId);
      obj.style.display = "none";
   }
   
   if (current_submenu == nr) {
      current_submenu = '';
   }
   else {
      current_submenu = nr;
   }
}