var new_window=0;
function close_window()
{
  if (new_window.closed==false) 
  new_window.close()
}

function openwin(datei,x,y)
{
  if (new_window!=0) close_window();
  new_window = open(datei,"Bild","width="+x+",height="+y+",resizable=no,scrollbars=no"); 
}