TLDR
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Kempelen chess puzzle: place four black queens and one black bishop so every square is attacked and the white king has no legal placement.
Key Takeaways
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The puzzle comes from Kempelen’s Mechanical Chess Player era and is framed as one of the hardest of those old chess problems.
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The goal is complete board coverage by four queens and one bishop, not standard mate against an existing king position.
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The source is interactive: drag or tap pieces onto the board, then test whether any square remains safe.
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The underlying constraint is combinatorial, since multiple piece placements can satisfy full attack coverage.
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The puzzle invites search or brute force reasoning as much as chess intuition.
Hacker News Comment Review
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Commenters focused on solution space, noting there are many valid placements and that the answers can look unintuitive.
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A practical implementation gripe emerged: manual “Check” clicks after every move slow down interactive experimentation.
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One commenter shared a Python-script mindset, suggesting the puzzle is approachable as a search problem, not just a human chess exercise.
Notable Comments
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@dllu: “388 solutions” and some solutions put three queens on the same row.
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@tantalor: wished the board would check automatically after each move.
Original | Discuss on HN
