FA-82914 / Go territory scoring / Member archive

Ko is declared although the capturing stone has several liberties · case 04

Snapback-style single captures with open points around are flagged as ko.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Input [board_after_move, row, col, captured_points]. A ko ban point exists only when exactly one stone was captured, the played stone has no friendly orthogonal neighbour, and it has exactly one liberty. Return the captured point or None.

Why this case matters

Go servers and scoring tools compute this value automatically; a wrong answer changes a game result.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
ko point case 4	`[2, 1]`	`null`	Failed

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