function $id(name) {
   return document.getElementById(name);
}

function foto_gross_klein (id_old, id_new, src_name) {
   $id(id_old).style.display = 'none';
   $id(id_new).style.display = 'block';
   if (src_name)
      { document.images[id_new].src = src_name; }
}

function toggleMenu(id) {
   var new_display_value;
   if ($id('menu' + id).style.display === 'block')
      { new_display_value = 'none'; }
   else 
      { new_display_value = 'block'; }
   $id('menu' + id).style.display = new_display_value;
}