FAILURE MAP
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FA-82891 / Go territory scoring / Open access

A capturing move into a surrounded point is rejected as suicide · case 01

Taking the last liberty of an enclosing chain is refused although it would capture.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The own-chain liberty check runs before opponent chains without liberties are removed.

THE FAILURE

The own-chain liberty check runs before opponent chains without liberties are removed.

Unsuccessful approach: Dropping the suicide test entirely accepts genuine suicides and leaves a libertyless chain on the board.

Case contract

Input [board, colour, row, col]. Occupied point -> ["illegal", "occupied"]. Otherwise place the stone, remove every adjacent opponent chain left without liberties, then reject the move as ["illegal", "suicide"] only if the placed chain still has no liberty. Return [new_board, captured_stone_count].

Why this case matters

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

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    board, color, r, c = x
    g = [list(row) for row in board]
    n = len(g)
    m = len(g[0])
    if g[r][c] != '.':
        return ['illegal', 'occupied']
    opp = 'W' if color == 'B' else 'B'
    g[r][c] = color
    def group(i, j):
        col = g[i][j]
        stones = {(i, j)}
        libs = set()
        stack = [(i, j)]
        while stack:
            a, b = stack.pop()
            for p, q in ((a, b + 1), (a + 1, b), (a, b - 1), (a - 1, b)):
                if 0 <= p < n and 0 <= q < m:
                    if g[p][q] == '.':
                        libs.add((p, q))
                    elif g[p][q] == col and (p, q) not in stones:
                        stones.add((p, q))
                        stack.append((p, q))
        return stones, libs
    own, own_libs = group(r, c)
    if not own_libs:
        return ['illegal', 'suicide']
    captured = 0
    for p, q in ((r + 1, c), (r - 1, c), (r, c + 1), (r, c - 1)):
        if 0 <= p < n and 0 <= q < m and g[p][q] == opp:
            stones, libs = group(p, q)
            if not libs:
                for s, t in stones:
                    g[s][t] = '.'
                captured += len(stones)
    stones, libs = group(r, c)
    if not libs:
        return ['illegal', 'suicide']
    return [[''.join(row) for row in g], captured]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[[['...', '...', '...'], 'W', 2, 0], [['...', '...', 'W..'], 0]], [[['.B.', 'B.B', '.B.'], 'W', 2, 2], ['illegal', 'suicide']], [[['.B.', 'B.B', '.B.'], 'W', 2, 0], ['illegal', 'suicide']], [[['.B.', 'B.B', '.B.'], 'B', 0, 0], [['BB.', 'B.B', '.B.'], 0]], [[['.B.', 'B.B', '.B.'], 'B', 0, 2], [['.BB', 'B.B', '.B.'], 0]], [[['.B.', 'B.B', '.B.'], 'B', 0, 1], ['illegal', 'occupied']], [[['WWBW', 'WBBW', 'WBB.'], 'W', 2, 3], [['WW.W', 'W..W', 'W..W'], 5]], [[['...', '.BW', '..B', '.BW', 'BB.'], 'W', 4, 2], ['illegal', 'suicide']]], [[[['B..W', 'B..W', 'B..W', 'B..W'], 'B', 1, 1], [['B..W', 'BB.W', 'B..W', 'B..W'], 0]], [[['B..W', 'B..W', 'B..W', 'B..W'], 'W', 0, 2], [['B.WW', 'B..W', 'B..W', 'B..W'], 0]], [[['B..W', 'B..W', 'B..W', 'B..W'], 'B', 0, 1], [['BB.W', 'B..W', 'B..W', 'B..W'], 0]], [[['B..W', 'B..W', 'B..W', 'B..W'], 'B', 2, 0], ['illegal', 'occupied']], [[['.BW.', '.BW.', '.BW.', '.BW.'], 'W', 2, 3], [['.BW.', '.BW.', '.BWW', '.BW.'], 0]], [[['.BW.', '.BW.', '.BW.', '.BW.'], 'W', 0, 0], [['WBW.', '.BW.', '.BW.', '.BW.'], 0]], [[['W.WW.', '...BW', '...W.'], 'B', 2, 4], ['illegal', 'suicide']], [[['WBW', 'BBB', 'BB.'], 'W', 2, 2], [['W.W', '...', '..W'], 6]]], [[[['.BW.', '.BW.', '.BW.', '.BW.'], 'B', 2, 0], [['.BW.', '.BW.', 'BBW.', '.BW.'], 0]], [[['.BW.', '.BW.', '.BW.', '.BW.'], 'B', 0, 2], ['illegal', 'occupied']], [[['..B..', '..B..', 'BBBBB', 'WWWWW', '..W..'], 'B', 0, 0], [['B.B..', '..B..', 'BBBBB', 'WWWWW', '..W..'], 0]], [[['..B..', '..B..', 'BBBBB', 'WWWWW', '..W..'], 'B', 1, 1], [['..B..', '.BB..', 'BBBBB', 'WWWWW', '..W..'], 0]], [[['..B..', '..B..', 'BBBBB', 'WWWWW', '..W..'], 'B', 4, 0], [['..B..', '..B..', 'BBBBB', 'WWWWW', 'B.W..'], 0]], [[['..B..', '..B..', 'BBBBB', 'WWWWW', '..W..'], 'B', 0, 1], [['.BB..', '..B..', 'BBBBB', 'WWWWW', '..W..'], 0]], [[['.B.', 'BWB', '...'], 'W', 0, 0], ['illegal', 'suicide']], [[['B.B', 'WBW', '.W.'], 'B', 2, 2], [['B.B', 'WB.', '.WB'], 1]]], [[[['B.B.W', '.B.W.', 'B.BW.', 'BBW.W', '..W..'], 'W', 2, 1], ['illegal', 'suicide']], [[['B.B.W', '.B.W.', 'B.BW.', 'BBW.W', '..W..'], 'W', 0, 1], ['illegal', 'suicide']], [[['B.B.W', '.B.W.', 'B.BW.', 'BBW.W', '..W..'], 'B', 4, 3], [['B.B.W', '.B.W.', 'B.BW.', 'BBW.W', '..WB.'], 0]], [[['B.B.W', '.B.W.', 'B.BW.', 'BBW.W', '..W..'], 'B', 2, 4], [['B.B.W', '.B.W.', 'B.BWB', 'BBW.W', '..W..'], 0]], [[['B.B.W', '.B.W.', 'B.BW.', 'BBW.W', '..W..'], 'B', 3, 2], ['illegal', 'occupied']], [[['W....', '.....', '.....', '.....', '....B'], 'W', 4, 1], [['W....', '.....', '.....', '.....', '.W..B'], 0]], [[['.W.', 'WBW', 'BWB'], 'B', 0, 2], [['.WB', 'WB.', 'BWB'], 1]], [[['BWB', 'W.W', 'BWB'], 'W', 1, 1], ['illegal', 'suicide']]], [[[['W....', '.....', '.....', '.....', '....B'], 'W', 3, 0], [['W....', '.....', '.....', 'W....', '....B'], 0]], [[['W....', '.....', '.....', '.....', '....B'], 'W', 4, 0], [['W....', '.....', '.....', '.....', 'W...B'], 0]], [[['W....', '.....', '.....', '.....', '....B'], 'B', 4, 4], ['illegal', 'occupied']], [[['.W.B.', 'W.WB.', '.WB..', 'WB...', 'B....'], 'W', 0, 2], [['.WWB.', 'W.WB.', '.WB..', 'WB...', 'B....'], 0]], [[['.W.B.', 'W.WB.', '.WB..', 'WB...', 'B....'], 'W', 0, 0], [['WW.B.', 'W.WB.', '.WB..', 'WB...', 'B....'], 0]], [[['.W.B.', 'W.WB.', '.WB..', 'WB...', 'B....'], 'B', 2, 4], [['.W.B.', 'W.WB.', '.WB.B', 'WB...', 'B....'], 0]], [[['WWW', 'W.W', 'WWW'], 'W', 1, 1], ['illegal', 'suicide']], [[['BWB', 'W.W', 'BWB'], 'B', 1, 1], [['B.B', '.B.', 'B.B'], 4]]]]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("move result case %d" % i, solve(args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
move result case 0[['...', '...', 'W..'], 0][['...', '...', 'W..'], 0]Passed
move result case 1['illegal', 'suicide']['illegal', 'suicide']Passed
move result case 2['illegal', 'suicide']['illegal', 'suicide']Passed
move result case 3[['BB.', 'B.B', '.B.'], 0][['BB.', 'B.B', '.B.'], 0]Passed
move result case 4[['.BB', 'B.B', '.B.'], 0][['.BB', 'B.B', '.B.'], 0]Passed
move result case 5['illegal', 'occupied']['illegal', 'occupied']Passed
move result case 6['illegal', 'suicide'][['WW.W', 'W..W', 'W..W'], 5]Failed
move result case 7['illegal', 'suicide']['illegal', 'suicide']Passed

SHA-256 / 2dc3464439bcb10837ec8d94e179acedd0d48ca81c6e2d5f732777a2e32b150a

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    board, color, r, c = x
    g = [list(row) for row in board]
    n = len(g)
    m = len(g[0])
    if g[r][c] != '.':
        return ['illegal', 'occupied']
    opp = 'W' if color == 'B' else 'B'
    g[r][c] = color
    def group(i, j):
        col = g[i][j]
        stones = {(i, j)}
        libs = set()
        stack = [(i, j)]
        while stack:
            a, b = stack.pop()
            for p, q in ((a, b + 1), (a + 1, b), (a, b - 1), (a - 1, b)):
                if 0 <= p < n and 0 <= q < m:
                    if g[p][q] == '.':
                        libs.add((p, q))
                    elif g[p][q] == col and (p, q) not in stones:
                        stones.add((p, q))
                        stack.append((p, q))
        return stones, libs
    captured = 0
    for p, q in ((r + 1, c), (r - 1, c), (r, c + 1), (r, c - 1)):
        if 0 <= p < n and 0 <= q < m and g[p][q] == opp:
            stones, libs = group(p, q)
            if not libs:
                for s, t in stones:
                    g[s][t] = '.'
                captured += len(stones)
    return [[''.join(row) for row in g], captured]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[[['...', '...', '...'], 'W', 2, 0], [['...', '...', 'W..'], 0]], [[['.B.', 'B.B', '.B.'], 'W', 2, 2], ['illegal', 'suicide']], [[['.B.', 'B.B', '.B.'], 'W', 2, 0], ['illegal', 'suicide']], [[['.B.', 'B.B', '.B.'], 'B', 0, 0], [['BB.', 'B.B', '.B.'], 0]], [[['.B.', 'B.B', '.B.'], 'B', 0, 2], [['.BB', 'B.B', '.B.'], 0]], [[['.B.', 'B.B', '.B.'], 'B', 0, 1], ['illegal', 'occupied']], [[['WWBW', 'WBBW', 'WBB.'], 'W', 2, 3], [['WW.W', 'W..W', 'W..W'], 5]], [[['...', '.BW', '..B', '.BW', 'BB.'], 'W', 4, 2], ['illegal', 'suicide']]], [[[['B..W', 'B..W', 'B..W', 'B..W'], 'B', 1, 1], [['B..W', 'BB.W', 'B..W', 'B..W'], 0]], [[['B..W', 'B..W', 'B..W', 'B..W'], 'W', 0, 2], [['B.WW', 'B..W', 'B..W', 'B..W'], 0]], [[['B..W', 'B..W', 'B..W', 'B..W'], 'B', 0, 1], [['BB.W', 'B..W', 'B..W', 'B..W'], 0]], [[['B..W', 'B..W', 'B..W', 'B..W'], 'B', 2, 0], ['illegal', 'occupied']], [[['.BW.', '.BW.', '.BW.', '.BW.'], 'W', 2, 3], [['.BW.', '.BW.', '.BWW', '.BW.'], 0]], [[['.BW.', '.BW.', '.BW.', '.BW.'], 'W', 0, 0], [['WBW.', '.BW.', '.BW.', '.BW.'], 0]], [[['W.WW.', '...BW', '...W.'], 'B', 2, 4], ['illegal', 'suicide']], [[['WBW', 'BBB', 'BB.'], 'W', 2, 2], [['W.W', '...', '..W'], 6]]], [[[['.BW.', '.BW.', '.BW.', '.BW.'], 'B', 2, 0], [['.BW.', '.BW.', 'BBW.', '.BW.'], 0]], [[['.BW.', '.BW.', '.BW.', '.BW.'], 'B', 0, 2], ['illegal', 'occupied']], [[['..B..', '..B..', 'BBBBB', 'WWWWW', '..W..'], 'B', 0, 0], [['B.B..', '..B..', 'BBBBB', 'WWWWW', '..W..'], 0]], [[['..B..', '..B..', 'BBBBB', 'WWWWW', '..W..'], 'B', 1, 1], [['..B..', '.BB..', 'BBBBB', 'WWWWW', '..W..'], 0]], [[['..B..', '..B..', 'BBBBB', 'WWWWW', '..W..'], 'B', 4, 0], [['..B..', '..B..', 'BBBBB', 'WWWWW', 'B.W..'], 0]], [[['..B..', '..B..', 'BBBBB', 'WWWWW', '..W..'], 'B', 0, 1], [['.BB..', '..B..', 'BBBBB', 'WWWWW', '..W..'], 0]], [[['.B.', 'BWB', '...'], 'W', 0, 0], ['illegal', 'suicide']], [[['B.B', 'WBW', '.W.'], 'B', 2, 2], [['B.B', 'WB.', '.WB'], 1]]], [[[['B.B.W', '.B.W.', 'B.BW.', 'BBW.W', '..W..'], 'W', 2, 1], ['illegal', 'suicide']], [[['B.B.W', '.B.W.', 'B.BW.', 'BBW.W', '..W..'], 'W', 0, 1], ['illegal', 'suicide']], [[['B.B.W', '.B.W.', 'B.BW.', 'BBW.W', '..W..'], 'B', 4, 3], [['B.B.W', '.B.W.', 'B.BW.', 'BBW.W', '..WB.'], 0]], [[['B.B.W', '.B.W.', 'B.BW.', 'BBW.W', '..W..'], 'B', 2, 4], [['B.B.W', '.B.W.', 'B.BWB', 'BBW.W', '..W..'], 0]], [[['B.B.W', '.B.W.', 'B.BW.', 'BBW.W', '..W..'], 'B', 3, 2], ['illegal', 'occupied']], [[['W....', '.....', '.....', '.....', '....B'], 'W', 4, 1], [['W....', '.....', '.....', '.....', '.W..B'], 0]], [[['.W.', 'WBW', 'BWB'], 'B', 0, 2], [['.WB', 'WB.', 'BWB'], 1]], [[['BWB', 'W.W', 'BWB'], 'W', 1, 1], ['illegal', 'suicide']]], [[[['W....', '.....', '.....', '.....', '....B'], 'W', 3, 0], [['W....', '.....', '.....', 'W....', '....B'], 0]], [[['W....', '.....', '.....', '.....', '....B'], 'W', 4, 0], [['W....', '.....', '.....', '.....', 'W...B'], 0]], [[['W....', '.....', '.....', '.....', '....B'], 'B', 4, 4], ['illegal', 'occupied']], [[['.W.B.', 'W.WB.', '.WB..', 'WB...', 'B....'], 'W', 0, 2], [['.WWB.', 'W.WB.', '.WB..', 'WB...', 'B....'], 0]], [[['.W.B.', 'W.WB.', '.WB..', 'WB...', 'B....'], 'W', 0, 0], [['WW.B.', 'W.WB.', '.WB..', 'WB...', 'B....'], 0]], [[['.W.B.', 'W.WB.', '.WB..', 'WB...', 'B....'], 'B', 2, 4], [['.W.B.', 'W.WB.', '.WB.B', 'WB...', 'B....'], 0]], [[['WWW', 'W.W', 'WWW'], 'W', 1, 1], ['illegal', 'suicide']], [[['BWB', 'W.W', 'BWB'], 'B', 1, 1], [['B.B', '.B.', 'B.B'], 4]]]]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("move result case %d" % i, solve(args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
move result case 0[['...', '...', 'W..'], 0][['...', '...', 'W..'], 0]Passed
move result case 1[['.B.', 'B.B', '.BW'], 0]['illegal', 'suicide']Failed
move result case 2[['.B.', 'B.B', 'WB.'], 0]['illegal', 'suicide']Failed
move result case 3[['BB.', 'B.B', '.B.'], 0][['BB.', 'B.B', '.B.'], 0]Passed
move result case 4[['.BB', 'B.B', '.B.'], 0][['.BB', 'B.B', '.B.'], 0]Passed
move result case 5['illegal', 'occupied']['illegal', 'occupied']Passed
move result case 6[['WW.W', 'W..W', 'W..W'], 5][['WW.W', 'W..W', 'W..W'], 5]Passed
move result case 7[['...', '.BW', '..B', '.BW', 'BBW'], 0]['illegal', 'suicide']Failed

SHA-256 / 6d8adcab3d3154adfd3ed1a58d98239351d1483b276fb41531b752dfdd1e40f7

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 8 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

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Verification & scope

Small rectangular toy boards given as strings of B, W and dot; a bounded teaching model of one scoring or bookkeeping rule, not a complete rules engine or server implementation. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:50:16.411653+00:00.

Case digest / 7cb675a4b58eb8a87c31267e71e1969f5bf35b78fef9ef07f0af988c8491a1e9