function highlight_lev(id) {
  var el = document.getElementById(id);
  var levimg = document.getElementById(id+'_img');
  levimg.src='img/'+id+'_img.jpg';
  el.setAttribute('class', 'highlight_lev');
}
function highlight_lev_r(id) {
  var el = document.getElementById(id);
  var levimg = document.getElementById(id+'_img');
  levimg.src='img/'+id+'_img_b.jpg';
  el.setAttribute('class', '');
}