var stayVisible;

function sichtbar(what){
 document.getElementById(what).style.visibility='visible';
}

function versteckt(what){
 if (stayVisible != what)
  document.getElementById(what).style.visibility='hidden';
}

function holdVisible(what){
 if (document.getElementById(stayVisible) != null)
  document.getElementById(stayVisible).style.visibility='hidden';
 stayVisible = what;
}