function toggle_visibility(id) {
       var e = document.getElementById(id);
	   var f = document.getElementById(id+'2');
       if(e.style.display == 'block')
	   {
          e.style.display = 'none';
		  f.innerHTML = '<a href="#" onClick="toggle_visibility(\'' + id + '\');return false"><img src="media/signomas.gif" width="15" height="14"></a>';
	   }
       else 
	   {
          e.style.display = 'block';
		  f.innerHTML = '<a href="#" onClick="toggle_visibility(\'' + id + '\');return false"><img src="media/signomenos.gif" width="15" height="14"></a>';
	   }
    }