FA-82664 / Chess move legality / Member archive

Enemy piece of the same type forces a disambiguator · case 04

With a black knight on f3, the white move Nb1-d2 is written "Nbd2".

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Input: {"board", "from", "to"} for a knight, bishop, rook, queen or king move. Return SAN (no check suffix): upper-case piece letter, then a disambiguator only if another same-colour piece of the same type could also reach the target (sliders need a clear path): the origin file if it is unique among those pieces, else the origin rank if unique, else the full origin square; then "x" if the target is occupied; then the target.

Why this case matters

Exported PGN must be re-readable; a wrong disambiguator makes the game unreplayable.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
enemy knight irrelevant	`"Nbd2"`	`"Nd2"`	Failed

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