This is the first in a series of three exercices de style to show some interesting aspects of the game of hats: a puzzle which was initially proposed by Lionel Levine, and arose from his work with Tobias Friedrich on
Eventually you will commit a huge file to your git repository by mistake. Use
git-filter-repo to remedy the situation.
Over the years, several tips and techniques have been developed to help solve sudoku puzzles with logic rather than brute force. To name a few, sudoku9x9 mentions (among others) hidden single, naked single, x-wing.