anchor.diff:  
     }
   
  +  boolean is_invited = Group_utils.has_been_invited(logged_in_user_id, gid);
  +  boolean is_a_member = Group_utils.is_member_of_group(logged_in_user_id, gid);
     boolean is_the_group_owner = logged_in_user_id == the_group.owner_id;
  +
  +
  +  if (!(is_invited || is_a_member)) {
  +    response.sendRedirect("general_error.jsp");
  +    return;
  +  }
  +
   %>
   	<body>
     <img id='my_background' src="img/front_screen.png" onload="xenos_utils.fade_in_background()"/>
  
positive.code: 
        <% } %>
  
        <% if (Group_utils.has_been_invited(logged_in_user_id, gid)) { %>
          <div>
            You have been invited to join this group.  Click on the button below to confirm joining
          </div>
  
negative.code:           </span>
      </div>
  
      <% if (is_a_member) { %>
        <div class="row">
          <label>Members:</label>
          <% for (java.util.Map.Entry<Integer, String> member : 
  