CHA-Solver
The tool to determine whether a player can be checkmated by any means, not necessarily by force, in a given chess position.
Required for fair timeout adjudication under FIDE Article 6.9.
Why does it matter?
When a player runs out of time, the game is almost always ruled a loss, but it is exceptionally declared a draw if their opponent cannot possibly checkmate them. Indeed, Article 6.9 of the FIDE Laws of Chess states:
“[...] the game is drawn if the position is such that the opponent cannot checkmate the player’s king by any possible series of legal moves.”
FIDE Laws of Chess, Article 6.9
Chess servers have historically ignored this rule, treating the problem as computationally intractable, leading to many wrongly decided games.
CHA-Solver is an efficient algorithm that decides with mathematical certainty whether a position is unwinnable.
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