function show(whichmenu) {
        // in case another menu is visible, hide all menus first.
       for ( i=1; i < 5; i++) {
           document.getElementById('menu' + i).style.visibility="hidden";
       }
   document.getElementById(whichmenu).style.visibility="visible";
}
	
function hidemenu(menu2Bclosed) {
   document.getElementById(menu2Bclosed).style.visibility="hidden";
}