var hidden = true;
function categories() {
 if (hidden)
 {
  document.getElementById('animals').style.visibility = 'visible';
  document.getElementById('transportation').style.visibility = 'visible';
  document.getElementById('people').style.visibility = 'visible';
  document.getElementById('still_life').style.visibility = 'visible';
  document.getElementById('categories').blur();
  hidden = false;
 } else {
  document.getElementById('animals').style.visibility = 'hidden';
  document.getElementById('transportation').style.visibility = 'hidden';
  document.getElementById('people').style.visibility = 'hidden';
  document.getElementById('still_life').style.visibility = 'hidden';
  document.getElementById('categories').blur();
  hidden = true;
 }
}

function show(what) {
 document.getElementById(what).style.visibility = 'visible';
 if (what != 'tnBig1')
  document.getElementById('tnBig1').style.visibility = 'hidden';
 if (what != 'tnBig2')
  document.getElementById('tnBig2').style.visibility = 'hidden';
 if (what != 'tnBig3')
  document.getElementById('tnBig3').style.visibility = 'hidden';
 if (what != 'tnBig4')
  document.getElementById('tnBig4').style.visibility = 'hidden';
}

function hide(what) {
 document.getElementById(what).style.visibility = 'hidden';
}