FA-82637 / Chess move legality / Member archive

Rank disambiguator compared with the file letter · case 02

"R1a3" is reported illegal although the a1 rook can play it.

Member previewVariant 2 · 3 implementations · 8 checks per implementation

Case contract

Input: {"board", "white": side to move, "san"} for a non-castling move. Check suffixes + and # are ignored. Resolve the SAN to the unique origin square of a pseudo-legal move (sliders need a clear path; pawns push one or, from their start rank through an empty square, two; pawns capture one step diagonally forward). "x" requires an enemy piece on the target and its absence requires an empty target. File/rank disambiguators filter candidates. Return the origin, "ambiguous" or "illegal".

Why this case matters

PGN import and move entry depend on resolving SAN to exactly one move.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
rook rank disambiguation	`"illegal"`	`"a1"`	Failed

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