var arrMenus = ['sm_1', 'sm_2', 'sm_3', 'sm_4'];            // neu, alle Submenü-IDs

function showlayer(layer)
{
   // --- Zusatz (schließt alle Submenüs) ---------------------
   for (idx in arrMenus)
      if(menu = document.getElementById(arrMenus[idx]))
         menu.style.display = "none";
   // --- Zusatz Ende ----------------------------------------- 
  
   var myLayer=document.getElementById(layer);
   
   if(myLayer.style.display=="none" || myLayer.style.display=="")
      myLayer.style.display="block";   
   else 
      myLayer.style.display="none";
}