This puzzle was inspired by Erich's Shape Grid.
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Acknowledgements and Changes
2022-02-26 Thanks to dohz for finding a subtle edge-case, now corrected.
2023-12-18 A regression found by justkirb was fixed - thank you!
2024-08-08 A mistake in the checker algorithm, reported a while ago by Justimagineit, who sent a good test case, was now corrected.
2025-03-23 A recent regression detected by 5381, on Unrectangles and Plot Twist, was corrected (cause: template misnaming)