Every puzzle in this app is a 27-clue grid with exactly one solution — verified in advance, so there's always a logical path through, never a guess required. "Diabolical" means every single puzzle needs genuinely advanced techniques — Singles, Pairs, Triples, and even X-Wings or Unique Rectangles alone won't crack any of them. Expect to lean on Y-Wings, W-Wings, or colour-based reasoning at minimum, and for most puzzles (77% of the set), full alternating inference chains like X-Cycles, XY-Chains, or AICs before they give way. On average that works out to about 12 non-Singles moves per puzzle — roughly double "Hard" and four times "Medium." One tier in this app climbs higher still: "Extreme," which averages even more chain-based reasoning than this one.
Paste 81 numbers, in almost any format: comma- or space-separated, a 9×9 grid, or one long string. Use 0 or . for empty cells — box-drawing separators (| and ---+---) are fine too.
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