function un_sichtbar(id) {
  var ref = "a" + id;
  if (document.getElementById(id).style.display == 'none') {
    document.getElementById(id).style.display = 'block';
    document.getElementById(ref).innerHTML = "zurück...";
    fake_height1(id);
  }
  else {
    document.getElementById(id).style.display = 'none'
    fake_height2();
    document.getElementById(ref).innerHTML = "mehr...";
  }
}
function fake_height1(id) {
  var src = document.getElementById(id);
  var dst =  document.getElementById('faketext');

  dst.innerHTML = src.innerHTML;
}

function fake_height2() {
  document.getElementById('faketext').innerHTML = "";
}
function openImpressum() {
  window.open('http://entwicklung.visualdesign-media.de/vds/vdi.html', 'VDI', 'width=230, height=350')
}