old_contents: 'use_strict';
  
  $(document).on("ready", function() {
    var version = "0.9"
  
    $('.lesson-preview a').click(function(e) {
      var lesson = $(this).attr('data-target');
      var lesson_index =  lesson.split("lesson")[1];
      if (lesson_index.length == 1) lesson_index = '0' + lesson_index;
      var lesson_link = 'http://zenlabs.pro/courses/lessons/' + lesson + '/lesson.pdf';
  //    var github_example_link = 'https://github.com/zzeni/swift_academy/tree/master/lessons/' + lesson + '/examples';
      var example_link = 'http://zenlabs.pro/courses/lessons/' + lesson + '/examples/index.html';
      var downlod_link = 'http://zenlabs.pro/courses/lessons/' + lesson + '/examples.zip';
      var homework_link = 'https://github.com/zzeni/swift-academy-homeworks/tree/master/tasks/L' + lesson_index;
      var homework_src = 'http://zenlabs.pro/courses/lessons/' + lesson + '/hw-task.html';
      
      lesson_link = lesson_link + "?version=" + version;
      downlod_link = downlod_link + "?version=" + version;
      
      $('.lesson-preview .selected').removeClass('selected');
      $(this).parent().addClass('selected');
      $('#lesson-name').text('Lesson ' + lesson_index);
      $('#presentation').attr('src', lesson_link);
      $('#presentation').parent().find('a:first').attr('href', lesson_link);
      $('#examples').attr('src', example_link);
      $('#examples').parent().find('a:first').attr('href', example_link);
  //    $('#examples').parent().find('a:last').attr('href', github_example_link);
      $('#examples').parent().find('a:last').attr('href', downlod_link);
      $('#homework-viewer').find('a:first').attr('href', homework_src);
      $('#hw-task').attr('src', homework_src);
      e.preventDefault();
    });
  
    $('.lesson-preview a:last-child').click();
  
    if ($('.lesson-preview ul').width() > $('.lesson-preview').width()) {
      var diff = $('.lesson-preview ul').width() - $('.lesson-preview').width() + 22;
      $(".lesson-preview").animate({ scrollLeft: diff }, 2000);
    }
  });
new_contents: 'use_strict';
  
  $(document).on("ready", function() {
    var version = "0.10"
  
    $('.lesson-preview a').click(function(e) {
      var lesson = $(this).attr('data-target');
      var lesson_index =  lesson.split("lesson")[1];
      if (lesson_index.length == 1) lesson_index = '0' + lesson_index;
      var lesson_link = 'http://zenlabs.pro/courses/lessons/' + lesson + '/lesson.pdf';
  //    var github_example_link = 'https://github.com/zzeni/swift_academy/tree/master/lessons/' + lesson + '/examples';
      var example_link = 'http://zenlabs.pro/courses/lessons/' + lesson + '/examples/index.html';
      var downlod_link = 'http://zenlabs.pro/courses/lessons/' + lesson + '/examples.zip';
      var homework_link = 'https://github.com/zzeni/swift-academy-homeworks/tree/master/tasks/L' + lesson_index;
      var homework_src = 'http://zenlabs.pro/courses/lessons/' + lesson + '/hw-task.html';
      
      lesson_link = lesson_link + "?version=" + version;
      downlod_link = downlod_link + "?version=" + version;
      
      $('.lesson-preview .selected').removeClass('selected');
      $(this).parent().addClass('selected');
      $('#lesson-name').text('Lesson ' + lesson_index);
      $('#presentation').attr('src', lesson_link);
      $('#presentation').parent().find('a:first').attr('href', lesson_link);
      $('#examples').attr('src', example_link);
      $('#examples').parent().find('a:first').attr('href', example_link);
  //    $('#examples').parent().find('a:last').attr('href', github_example_link);
      $('#examples').parent().find('a:last').attr('href', downlod_link);
      $('#homework-viewer').find('a:first').attr('href', homework_src);
      $('#hw-task').attr('src', homework_src);
      e.preventDefault();
    });
  
    $('.lesson-preview a:last-child').click();
  
    if ($('.lesson-preview ul').width() > $('.lesson-preview').width()) {
      var diff = $('.lesson-preview ul').width() - $('.lesson-preview').width() + 22;
      $(".lesson-preview").animate({ scrollLeft: diff }, 2000);
    }
  });
subject: add refs to lesson 16