I found that doing easy and medium Sudoku in pen is remarkably enjoyable, far more so than it ever was when I would make temporary marks.  It&#x27;s harder, and I&#x27;m not very good at Sudoku in general, but it really reinforces the &quot;you have to prove it ...&quot; mindset.  Strangely, even though I am slower, I seem to get stuck less often.