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# Notes on Chapter 4 – Recursion > From Clean Architecture , page 112

Let’s be honest: flipping through a 900-page PDF programming book while trying to write code is a pain. Alt-tabbing between a heavy PDF reader and your editor breaks flow. Highlighting is clunky. And copying code samples? They come with page numbers, weird line breaks, and sometimes even copyright notices embedded in the text.

The dependency rule is actually simpler than I thought:

## Pro Tips for Power Users

# My reimplementation class BoundaryInterface: pass </code></pre> <p><strong>TODO</strong>: Refactor my payment service using this pattern.</p> <pre><code> Pin the Markdown preview next to the PDF using the `View: Split Editor Right` command.

*Have a favorite PDF or book you always keep open in VS Code? Reply and let me know—I’m always looking for the next great recommendation.* </code></pre>