function inverseDisplayPresentation2() {
  if(document.getElementById('presentation2').style.display != 'block' ) {
    document.getElementById('presentation2').style.display = 'block';
  }
  else {
    document.getElementById('presentation2').style.display = 'none';
  }
}

function show(id) {
  document.getElementById(id).style.display = 'block';
}
function hide(id) {
  document.getElementById(id).style.display = 'none';
}