Very good article, I enjoyed reading it. I spotted something out of place - might be just me though - on first page you have a "Lesson 1" heading at the top of article and "Lesson 2" heading at the bottom of article, which is fine.
When I go to page no. 2, it starts with "Lesson 1" heading and then it proceeds to "Lesson 3" heading. Was it meant to be that way, or was the author meant to add Lesson 2 there, or remove Lesson 1 from top, to continue from 1st page?