function tricker(a) {
  var e=document.getElementById(a);
  var pic=document.getElementById("pfeil"+a.toString());
    
  if(!e)return true;
  if(e.style.display=="none"){
    e.style.display="block";
    pic.src="images/pfeil_down.jpg";
  } else {
    e.style.display="none";
    pic.src="images/pfeil_left.jpg";
  }
  return true;
}