What are the solving lessons?

With "Solving lessons" on, the book gets one page for every solving technique its puzzles need, after How to play. Each page names the technique, explains it in plain words and shows it on a real position from one of the book's own puzzles, with the pencil marks that tell the story, the pattern's squares shaded, the removed marks struck through and a placed number circled. The caption says which puzzle and page it comes from and what happens.