FA-82846 / Go territory scoring / Open access

Dame bordered by both colours is credited to black · case 01

Neutral points between the two armies are added to black area and the reported margin is inflated.

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

ROOT CAUSE

Ownership tests whether a colour appears in the border set instead of requiring the border to be exactly that colour.

VERIFIED REPAIR

Credit a region only when its border set equals {B} or equals {W}.

Unsuccessful approach: A subset test fixes shared dame but credits the fully empty board (empty border set) to black.

Case contract

Input [board, komi_tenths]. Area = own stones + empty regions whose orthogonal border touches only that colour. Return [black_area, white_area, result] where result is "B+x.y" / "W+x.y" after subtracting komi from black, or "Draw".

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, komi = x
    n = len(board)
    m = len(board[0])
    b = sum(row.count('B') for row in board)
    w = sum(row.count('W') for row in board)
    seen = set()
    for r in range(n):
        for c in range(m):
            if board[r][c] != '.' or (r, c) in seen:
                continue
            stack = [(r, c)]
            seen.add((r, c))
            size = 0
            border = set()
            while stack:
                i, j = stack.pop()
                size += 1
                for di, dj in ((1, 0), (-1, 0), (0, 1), (0, -1)):
                    a, d = i + di, j + dj
                    if 0 <= a < n and 0 <= d < m:
                        v = board[a][d]
                        if v == '.':
                            if (a, d) not in seen:
                                seen.add((a, d))
                                stack.append((a, d))
                        else:
                            border.add(v)
            if 'B' in border:
                b += size
            elif 'W' in border:
                w += size
    diff = b * 10 - w * 10 - komi
    if diff > 0:
        res = 'B+%d.%d' % (diff // 10, diff % 10)
    elif diff < 0:
        res = 'W+%d.%d' % ((-diff) // 10, (-diff) % 10)
    else:
        res = 'Draw'
    return [b, w, res]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[[['...', '...', '...'], 5], [0, 0, 'W+0.5']], [[['B..W', 'B..W', 'B..W', 'B..W'], 75], [4, 4, 'W+7.5']], [[['BBBB', 'B..B', 'B..B', 'BBBB'], 5], [16, 0, 'B+15.5']], [[['WWW', 'W.W', 'WWW'], 65], [0, 9, 'W+15.5']], [[['B.W', '...', 'W.B'], 75], [2, 2, 'W+7.5']], [[['.B...', 'B....', '.....', '....W', '...W.'], 35], [3, 3, 'W+3.5']], [[['BW.', 'BW.', 'BW.'], 60], [3, 6, 'W+9.0']], [[['.....', '.BBB.', '.B.B.', '.BBB.', '.....'], 70], [25, 0, 'B+18.0']]], [[[['...', '...', '...'], 5], [0, 0, 'W+0.5']], [[['.W.B.', 'W.WB.', '.WB..', 'WB...', 'B....'], 0], [16, 8, 'B+8.0']], [[['..W', '.W.', 'W..'], 0], [0, 9, 'W+9.0']], [[['B....B', '......', '..WW..', '..WW..', '......', 'B....B'], 5], [4, 4, 'W+0.5']], [[['.BBW.', 'B.BBB', '...W.', '.B.WB'], 65], [9, 3, 'W+0.5']], [[['BB.W.', 'BB.WW', 'W..WW', '.W...', '.B...'], 75], [5, 8, 'W+10.5']], [[['B..', '..W', '...', '.WW'], 35], [1, 3, 'W+5.5']], [[['...B..', '.B..B.', '..W...', 'B..B..'], 60], [5, 1, 'W+2.0']]], [[[['...', '...', '...'], 5], [0, 0, 'W+0.5']], [[['B....B', '......', '..WW..', '..WW..', '......', 'B....B'], 5], [4, 4, 'W+0.5']], [[['WBWWB', 'BB.B.', 'WBWB.', 'WBWBB'], -5], [12, 7, 'B+5.5']], [[['...', '...', '.B.', '.WB', '...', 'B..'], 0], [3, 1, 'B+2.0']], [[['.....', '.W...', 'WW...'], 5], [0, 15, 'W+15.5']], [[['.B.', '.WW', 'BBB', 'WW.'], 65], [4, 4, 'W+6.5']], [[['.B.BB', 'WB...', '.....'], 75], [4, 1, 'W+4.5']], [[['.WBB', 'BW..', '..B.'], 35], [4, 2, 'W+1.5']]], [[[['...', '...', '...'], 5], [0, 0, 'W+0.5']], [[['B..', '..W', '...', '.WW'], 35], [1, 3, 'W+5.5']], [[['B..', '.B.', '...', '...', 'B..', 'BB.'], 70], [18, 0, 'B+11.0']], [[['BW.B', '.WWW', 'B.BB', 'WBB.', 'BW.W'], -5], [8, 7, 'B+1.5']], [[['......', '..W...', 'WW.WW.', '......', 'WBW...'], 0], [1, 7, 'W+6.0']], [[['W..W', '.B..', 'B.W.', '.W..', '....'], 5], [2, 4, 'W+2.5']], [[['BWBB.', '.B..B', 'BW..B', 'W.BBW', '...BB'], 65], [13, 4, 'B+2.5']], [[['...W..', '..WBW.', 'W...WW', '.WW..W'], 75], [1, 13, 'W+19.5']]], [[[['...', '...', '...'], 5], [0, 0, 'W+0.5']], [[['WBWWB', 'BB.B.', 'WBWB.', 'WBWBB'], -5], [12, 7, 'B+5.5']], [[['W..B.', 'BB.BB', 'B..B.', 'BBB..', 'B.BBB'], 60], [19, 1, 'B+12.0']], [[['.BBBW.', 'WBBBB.', '.WBB..', 'BBB...', 'BBW..B', '..BW.W'], 70], [18, 6, 'B+5.0']], [[['W..BBB', 'BWB.W.', '.WWWWW', 'W.WBWW'], -5], [6, 13, 'W+6.5']], [[['W..B', '...B', 'WWWW'], 0], [2, 5, 'W+3.0']], [[['W...', 'WBWB', 'WWBW', 'BBB.'], 5], [6, 6, 'W+0.5']], [[['WW..', 'WWW.', 'BWWW'], 65], [1, 11, 'W+16.5']]]]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("area score 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 fixture	Actual	Expected	Outcome
area score case 0	`[0, 0, 'W+0.5']`	`[0, 0, 'W+0.5']`	Passed
area score case 1	`[12, 4, 'B+0.5']`	`[4, 4, 'W+7.5']`	Failed
area score case 2	`[16, 0, 'B+15.5']`	`[16, 0, 'B+15.5']`	Passed
area score case 3	`[0, 9, 'W+15.5']`	`[0, 9, 'W+15.5']`	Passed
area score case 4	`[7, 2, 'W+2.5']`	`[2, 2, 'W+7.5']`	Failed
area score case 5	`[22, 3, 'B+15.5']`	`[3, 3, 'W+3.5']`	Failed
area score case 6	`[3, 6, 'W+9.0']`	`[3, 6, 'W+9.0']`	Passed
area score case 7	`[25, 0, 'B+18.0']`	`[25, 0, 'B+18.0']`	Passed

SHA-256 / bf32d89ec8abc048ba7f51c577f8d16054ac46a5eec028767a0836a8b2fd8467

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(x):
    board, komi = x
    n = len(board)
    m = len(board[0])
    b = sum(row.count('B') for row in board)
    w = sum(row.count('W') for row in board)
    seen = set()
    for r in range(n):
        for c in range(m):
            if board[r][c] != '.' or (r, c) in seen:
                continue
            stack = [(r, c)]
            seen.add((r, c))
            size = 0
            border = set()
            while stack:
                i, j = stack.pop()
                size += 1
                for di, dj in ((1, 0), (-1, 0), (0, 1), (0, -1)):
                    a, d = i + di, j + dj
                    if 0 <= a < n and 0 <= d < m:
                        v = board[a][d]
                        if v == '.':
                            if (a, d) not in seen:
                                seen.add((a, d))
                                stack.append((a, d))
                        else:
                            border.add(v)
            if border <= {'B'}:
                b += size
            elif border <= {'W'}:
                w += size
    diff = b * 10 - w * 10 - komi
    if diff > 0:
        res = 'B+%d.%d' % (diff // 10, diff % 10)
    elif diff < 0:
        res = 'W+%d.%d' % ((-diff) // 10, (-diff) % 10)
    else:
        res = 'Draw'
    return [b, w, res]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[[['...', '...', '...'], 5], [0, 0, 'W+0.5']], [[['B..W', 'B..W', 'B..W', 'B..W'], 75], [4, 4, 'W+7.5']], [[['BBBB', 'B..B', 'B..B', 'BBBB'], 5], [16, 0, 'B+15.5']], [[['WWW', 'W.W', 'WWW'], 65], [0, 9, 'W+15.5']], [[['B.W', '...', 'W.B'], 75], [2, 2, 'W+7.5']], [[['.B...', 'B....', '.....', '....W', '...W.'], 35], [3, 3, 'W+3.5']], [[['BW.', 'BW.', 'BW.'], 60], [3, 6, 'W+9.0']], [[['.....', '.BBB.', '.B.B.', '.BBB.', '.....'], 70], [25, 0, 'B+18.0']]], [[[['...', '...', '...'], 5], [0, 0, 'W+0.5']], [[['.W.B.', 'W.WB.', '.WB..', 'WB...', 'B....'], 0], [16, 8, 'B+8.0']], [[['..W', '.W.', 'W..'], 0], [0, 9, 'W+9.0']], [[['B....B', '......', '..WW..', '..WW..', '......', 'B....B'], 5], [4, 4, 'W+0.5']], [[['.BBW.', 'B.BBB', '...W.', '.B.WB'], 65], [9, 3, 'W+0.5']], [[['BB.W.', 'BB.WW', 'W..WW', '.W...', '.B...'], 75], [5, 8, 'W+10.5']], [[['B..', '..W', '...', '.WW'], 35], [1, 3, 'W+5.5']], [[['...B..', '.B..B.', '..W...', 'B..B..'], 60], [5, 1, 'W+2.0']]], [[[['...', '...', '...'], 5], [0, 0, 'W+0.5']], [[['B....B', '......', '..WW..', '..WW..', '......', 'B....B'], 5], [4, 4, 'W+0.5']], [[['WBWWB', 'BB.B.', 'WBWB.', 'WBWBB'], -5], [12, 7, 'B+5.5']], [[['...', '...', '.B.', '.WB', '...', 'B..'], 0], [3, 1, 'B+2.0']], [[['.....', '.W...', 'WW...'], 5], [0, 15, 'W+15.5']], [[['.B.', '.WW', 'BBB', 'WW.'], 65], [4, 4, 'W+6.5']], [[['.B.BB', 'WB...', '.....'], 75], [4, 1, 'W+4.5']], [[['.WBB', 'BW..', '..B.'], 35], [4, 2, 'W+1.5']]], [[[['...', '...', '...'], 5], [0, 0, 'W+0.5']], [[['B..', '..W', '...', '.WW'], 35], [1, 3, 'W+5.5']], [[['B..', '.B.', '...', '...', 'B..', 'BB.'], 70], [18, 0, 'B+11.0']], [[['BW.B', '.WWW', 'B.BB', 'WBB.', 'BW.W'], -5], [8, 7, 'B+1.5']], [[['......', '..W...', 'WW.WW.', '......', 'WBW...'], 0], [1, 7, 'W+6.0']], [[['W..W', '.B..', 'B.W.', '.W..', '....'], 5], [2, 4, 'W+2.5']], [[['BWBB.', '.B..B', 'BW..B', 'W.BBW', '...BB'], 65], [13, 4, 'B+2.5']], [[['...W..', '..WBW.', 'W...WW', '.WW..W'], 75], [1, 13, 'W+19.5']]], [[[['...', '...', '...'], 5], [0, 0, 'W+0.5']], [[['WBWWB', 'BB.B.', 'WBWB.', 'WBWBB'], -5], [12, 7, 'B+5.5']], [[['W..B.', 'BB.BB', 'B..B.', 'BBB..', 'B.BBB'], 60], [19, 1, 'B+12.0']], [[['.BBBW.', 'WBBBB.', '.WBB..', 'BBB...', 'BBW..B', '..BW.W'], 70], [18, 6, 'B+5.0']], [[['W..BBB', 'BWB.W.', '.WWWWW', 'W.WBWW'], -5], [6, 13, 'W+6.5']], [[['W..B', '...B', 'WWWW'], 0], [2, 5, 'W+3.0']], [[['W...', 'WBWB', 'WWBW', 'BBB.'], 5], [6, 6, 'W+0.5']], [[['WW..', 'WWW.', 'BWWW'], 65], [1, 11, 'W+16.5']]]]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("area score 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 fixture	Actual	Expected	Outcome
area score case 0	`[9, 0, 'B+8.5']`	`[0, 0, 'W+0.5']`	Failed
area score case 1	`[4, 4, 'W+7.5']`	`[4, 4, 'W+7.5']`	Passed
area score case 2	`[16, 0, 'B+15.5']`	`[16, 0, 'B+15.5']`	Passed
area score case 3	`[0, 9, 'W+15.5']`	`[0, 9, 'W+15.5']`	Passed
area score case 4	`[2, 2, 'W+7.5']`	`[2, 2, 'W+7.5']`	Passed
area score case 5	`[3, 3, 'W+3.5']`	`[3, 3, 'W+3.5']`	Passed
area score case 6	`[3, 6, 'W+9.0']`	`[3, 6, 'W+9.0']`	Passed
area score case 7	`[25, 0, 'B+18.0']`	`[25, 0, 'B+18.0']`	Passed

SHA-256 / 6b671a6d7b69b9c1d72003c1da5f0eeb2712ffa071a025ac99025d477d1fb70f

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(x):
    board, komi = x
    n = len(board)
    m = len(board[0])
    b = sum(row.count('B') for row in board)
    w = sum(row.count('W') for row in board)
    seen = set()
    for r in range(n):
        for c in range(m):
            if board[r][c] != '.' or (r, c) in seen:
                continue
            stack = [(r, c)]
            seen.add((r, c))
            size = 0
            border = set()
            while stack:
                i, j = stack.pop()
                size += 1
                for di, dj in ((1, 0), (-1, 0), (0, 1), (0, -1)):
                    a, d = i + di, j + dj
                    if 0 <= a < n and 0 <= d < m:
                        v = board[a][d]
                        if v == '.':
                            if (a, d) not in seen:
                                seen.add((a, d))
                                stack.append((a, d))
                        else:
                            border.add(v)
            if border == {'B'}:
                b += size
            elif border == {'W'}:
                w += size
    diff = b * 10 - w * 10 - komi
    if diff > 0:
        res = 'B+%d.%d' % (diff // 10, diff % 10)
    elif diff < 0:
        res = 'W+%d.%d' % ((-diff) // 10, (-diff) % 10)
    else:
        res = 'Draw'
    return [b, w, res]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[[['...', '...', '...'], 5], [0, 0, 'W+0.5']], [[['B..W', 'B..W', 'B..W', 'B..W'], 75], [4, 4, 'W+7.5']], [[['BBBB', 'B..B', 'B..B', 'BBBB'], 5], [16, 0, 'B+15.5']], [[['WWW', 'W.W', 'WWW'], 65], [0, 9, 'W+15.5']], [[['B.W', '...', 'W.B'], 75], [2, 2, 'W+7.5']], [[['.B...', 'B....', '.....', '....W', '...W.'], 35], [3, 3, 'W+3.5']], [[['BW.', 'BW.', 'BW.'], 60], [3, 6, 'W+9.0']], [[['.....', '.BBB.', '.B.B.', '.BBB.', '.....'], 70], [25, 0, 'B+18.0']]], [[[['...', '...', '...'], 5], [0, 0, 'W+0.5']], [[['.W.B.', 'W.WB.', '.WB..', 'WB...', 'B....'], 0], [16, 8, 'B+8.0']], [[['..W', '.W.', 'W..'], 0], [0, 9, 'W+9.0']], [[['B....B', '......', '..WW..', '..WW..', '......', 'B....B'], 5], [4, 4, 'W+0.5']], [[['.BBW.', 'B.BBB', '...W.', '.B.WB'], 65], [9, 3, 'W+0.5']], [[['BB.W.', 'BB.WW', 'W..WW', '.W...', '.B...'], 75], [5, 8, 'W+10.5']], [[['B..', '..W', '...', '.WW'], 35], [1, 3, 'W+5.5']], [[['...B..', '.B..B.', '..W...', 'B..B..'], 60], [5, 1, 'W+2.0']]], [[[['...', '...', '...'], 5], [0, 0, 'W+0.5']], [[['B....B', '......', '..WW..', '..WW..', '......', 'B....B'], 5], [4, 4, 'W+0.5']], [[['WBWWB', 'BB.B.', 'WBWB.', 'WBWBB'], -5], [12, 7, 'B+5.5']], [[['...', '...', '.B.', '.WB', '...', 'B..'], 0], [3, 1, 'B+2.0']], [[['.....', '.W...', 'WW...'], 5], [0, 15, 'W+15.5']], [[['.B.', '.WW', 'BBB', 'WW.'], 65], [4, 4, 'W+6.5']], [[['.B.BB', 'WB...', '.....'], 75], [4, 1, 'W+4.5']], [[['.WBB', 'BW..', '..B.'], 35], [4, 2, 'W+1.5']]], [[[['...', '...', '...'], 5], [0, 0, 'W+0.5']], [[['B..', '..W', '...', '.WW'], 35], [1, 3, 'W+5.5']], [[['B..', '.B.', '...', '...', 'B..', 'BB.'], 70], [18, 0, 'B+11.0']], [[['BW.B', '.WWW', 'B.BB', 'WBB.', 'BW.W'], -5], [8, 7, 'B+1.5']], [[['......', '..W...', 'WW.WW.', '......', 'WBW...'], 0], [1, 7, 'W+6.0']], [[['W..W', '.B..', 'B.W.', '.W..', '....'], 5], [2, 4, 'W+2.5']], [[['BWBB.', '.B..B', 'BW..B', 'W.BBW', '...BB'], 65], [13, 4, 'B+2.5']], [[['...W..', '..WBW.', 'W...WW', '.WW..W'], 75], [1, 13, 'W+19.5']]], [[[['...', '...', '...'], 5], [0, 0, 'W+0.5']], [[['WBWWB', 'BB.B.', 'WBWB.', 'WBWBB'], -5], [12, 7, 'B+5.5']], [[['W..B.', 'BB.BB', 'B..B.', 'BBB..', 'B.BBB'], 60], [19, 1, 'B+12.0']], [[['.BBBW.', 'WBBBB.', '.WBB..', 'BBB...', 'BBW..B', '..BW.W'], 70], [18, 6, 'B+5.0']], [[['W..BBB', 'BWB.W.', '.WWWWW', 'W.WBWW'], -5], [6, 13, 'W+6.5']], [[['W..B', '...B', 'WWWW'], 0], [2, 5, 'W+3.0']], [[['W...', 'WBWB', 'WWBW', 'BBB.'], 5], [6, 6, 'W+0.5']], [[['WW..', 'WWW.', 'BWWW'], 65], [1, 11, 'W+16.5']]]]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("area score 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 fixture	Actual	Expected	Outcome
area score case 0	`[0, 0, 'W+0.5']`	`[0, 0, 'W+0.5']`	Passed
area score case 1	`[4, 4, 'W+7.5']`	`[4, 4, 'W+7.5']`	Passed
area score case 2	`[16, 0, 'B+15.5']`	`[16, 0, 'B+15.5']`	Passed
area score case 3	`[0, 9, 'W+15.5']`	`[0, 9, 'W+15.5']`	Passed
area score case 4	`[2, 2, 'W+7.5']`	`[2, 2, 'W+7.5']`	Passed
area score case 5	`[3, 3, 'W+3.5']`	`[3, 3, 'W+3.5']`	Passed
area score case 6	`[3, 6, 'W+9.0']`	`[3, 6, 'W+9.0']`	Passed
area score case 7	`[25, 0, 'B+18.0']`	`[25, 0, 'B+18.0']`	Passed

SHA-256 / cbb24f94c7d5119ebca72e4b1777b81563e0079ecddb0e81c888c352ea59f1cb

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 2026-09-29T14:50:15.939477+00:00.

Case digest / 6a05bce3877a062bfff321cac6e5d5a7e1d4163804fe378c2431d348c8f4e070