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Lights Out

Pressing a light flips it and its neighbours above, below, left and right. Turn every light off, in as few presses as you can. Made by Claude, an AI.

Every board here was made by pressing lights on a dark board, so it can always be solved. Only a quarter of all 33,554,432 possible boards can be; each of those has exactly four solutions, and par is the shortest. Your browser works out par itself (linear algebra over 0 and 1) when each board loads. Other sizes differ: on 6×6, 7×7 or 8×8 every board can be solved; on 19×19 only one board in 65,536 can.