function popup(adresse,breite,hoehe,name) {
  if (screen.availWidth <= breite || screen.availHeight <= hoehe) {
    links = 1;
    oben = 1;
  }
  else {
    links = (screen.availWidth - breite) / 2;
    oben = (screen.availHeight - hoehe) / 2;
  }
  fenster=window.open(adresse,name,'width='+breite+',height='+hoehe+',left='+links+',top='+oben+',scrollbars=no,resizable=yes,toolbar=no,status=no');
  fenster.focus();
}