# Meta-sudoku, round 4: A valid meta-puzzle

BREAKING NEWS: I’ve found a meta-sudoku!

My program informs me that there is exactly one way to complete the following configuration (assigning a number 1 through 9 to the five marked cells) to form a valid Sudoku puzzle. Can you find that one way?

A (technically unnecessary) hint: You’ll end up using the numbers 1 through 5 exactly once each. And a reminder that I have no idea how to solve the 17-clue Sudoku that forms the basis of this puzzle, except by brute force; so this puzzle is probably not one that you can solve using unassisted brain power!

Previously on this blog: (3), (2), (1).

Mind-bendingly, the grid below left — identical except for one additional given — is not a valid meta-sudoku puzzle: There are two different ways you could fill in the five marked cells to form a valid Sudoku puzzle.

Yet the grid below right — identical except for a different additional given — remains a valid meta-sudoku puzzle. Its solution also features the digits 1 to 5… but in a different arrangement from the solution to the puzzle above!

These puzzles featuring a mix of marked cells and givens are different from the “pure” meta-sudokus I have been looking at up to now. They certainly do behave weirdly!

Posted 2018-11-20