function collapse(aktualis, darab) {
  for (i=1;i<=darab;i++) {
    document.getElementById(i).style.display = "none";
    document.getElementById("a" + i).style.fontWeight = "normal";
  }
  document.getElementById(aktualis).style.display = "block";
  document.getElementById("a" + aktualis).style.fontWeight = "bold";
}