function getMain() {
  if(window.ActiveXObject) {
    try {
      xmlhttp1 = new ActiveXObject("Msxml2.xmlhttp");
    } catch (e) {
      try {
        xmlhttp1 = new ActiveXObject("Microsoft.xmlhttp");
      } catch (e) {
        xmlhttp1 = false;
      }
    }
  } else if(window.XMLHttpRequest) {
    xmlhttp1 = new XMLHttpRequest();
  } else {
    xmlhttp1 = false;
  }
  if(xmlhttp1) {
    xmlhttp1.onreadystatechange = function() {
      if(xmlhttp1.readyState == 4 && xmlhttp1.status == 200) {
        var disp = document.getElementById('main-lesson');
        var html = xmlhttp1.responseText;
        disp.innerHTML = html;
      }
    }
    xmlhttp1.open('GET', 'main_list.php');
    xmlhttp1.send(null);
  }
}

function getGenre(genre_tier,genre_id) {
  if(window.ActiveXObject) {
    try {
      xmlhttp2 = new ActiveXObject("Msxml2.xmlhttp");
    } catch (e) {
      try {
        xmlhttp2 = new ActiveXObject("Microsoft.xmlhttp");
      } catch (e) {
        xmlhttp2 = false;
      }
    }
  } else if(window.XMLHttpRequest) {
    xmlhttp2 = new XMLHttpRequest();
  } else {
    xmlhttp2 = false;
  }
  if(xmlhttp2) {
    xmlhttp2.onreadystatechange = function() {
      if(xmlhttp2.readyState == 4 && xmlhttp2.status == 200) {
        var disp = document.getElementById('main-lesson-genre');
        var html = xmlhttp2.responseText;
        disp.innerHTML = html;
      }
    }
    xmlhttp2.open('GET', 'genre_list.php?t=' + genre_tier + '&g=' + genre_id);
    xmlhttp2.send(null);
  }
}