FA-82514 / Chess move legality / Member archive

Pinned bishop may switch to another line through its king · case 04

A bishop pinned on the c1-g5 diagonal may move to c3 or e1.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Input: {"board", "from": square of a non-king piece, "to": its pseudo-legal destination}. Return false only when the piece is absolutely pinned (it is the first piece on a line from its own king and the next piece beyond it on that line is an enemy rook/queen on a rank or file, or bishop/queen on a diagonal) and the destination leaves that line; moves along the pin line, including capturing the pinner, return true.

Why this case matters

Move validators gate every move in engines, servers and arbiters; accepting an illegal move or rejecting a legal one corrupts the game record.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
diagonal pinned bishop off line	`true`	`false`	Failed

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This record includes three runnable implementations, regression fixtures, execution results, and source hashes.

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