Why is a perpetual chase claim generally harder to prove than a perpetual check claim?
These answers restate the rules implemented by our open-source engine, which follows the WXF laws for movement, checkmate and both repetition rulings: a side that forces a repetition by perpetual check or perpetual chase loses rather than drawing. The chase half has not been validated against the official casebook. Where an answer refers to a specific position, that position lives on the linked reference page, where the build verifies it before publishing.
Direct answer
Because check is one fact and chase is several tests. Whether a move attacks the general is unambiguous: it either gives check or it does not. Whether a piece is being chased depends on several questions about the board: was the same piece threatened on every move, was it protected, would taking it still win material, and was the attacker the general or a soldier, which never count. Each can be a close call.
What makes check simple to adjudicate
A perpetual check claim only needs the moves of the repeated sequence: did one side give check on every one of its moves? Nothing about the purpose of those moves matters, only the bare fact that each one attacked the general.
What makes chase genuinely harder
A chase claim requires asking whether it was the same piece under threat on every move, whether that piece was protected, whether taking it would still have won material, and whether a check anywhere in the sequence changes the ruling. Protection is the hardest part: a move can remove a defender, and whether the piece then counts as protected depends on which moment you judge it from. Those are exactly the kind of borderline cases that led to the WXF building a casebook of worked examples rather than trying to write one clean rule that covers everything.
Related questions
Is this why some cases are still genuinely disputed even among strong engines?
Yes, a handful of classic diagrams in the casebook are known to be judged differently by different strong engines, precisely because of this ambiguity.
Does this mean perpetual chase rulings are inconsistent?
Not inconsistent exactly, but they rely on precedent and judgement in a way perpetual check simply does not need to.
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