FA-72731 / Check-digit algorithms / Open access

Container category admits only freight containers · case 01

Detachable-equipment (J) and trailer (Z) identifiers are rejected.

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

ROOT CAUSE

The category test accepts only U.

VERIFIED REPAIR

Accept equipment categories U, J and Z.

Unsuccessful approach: Adding J but not Z still rejects trailers and chassis.

Case contract

Shipping container identification check digit: three uppercase owner letters, category U, J or Z, six serial digits and a check digit (else "malformed"). Letter values start at A=10 and skip every multiple of 11 (so B=12, L=23, V=34, Z=38). Position i (0-based) has weight 2^i; the check digit is (sum mod 11) mod 10. Return [check, match].

Why this case matters

Terminal gate systems validate container numbers read by OCR cameras before booking moves.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(s):
    if len(s) != 11 or not s.isascii() or not s[:3].isalpha() or not s[:3].isupper():
        return 'malformed'
    if s[3] != 'U' or not s[4:].isdigit():
        return 'malformed'
    vals = {}
    v = 10
    for ch in 'ABCDEFGHIJKLMNOPQRSTUVWXYZ':
        if v % 11 == 0:
            v += 1
        vals[ch] = v
        v += 1
    total = 0
    for i, ch in enumerate(s[:10]):
        total += (vals[ch] if ch.isalpha() else int(ch)) * 2 ** i
    check = total % 11 % 10
    return [check, check == int(s[10])]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression ["BYYJ6917585"]', ['BYYJ6917585'], [8, False]], ['regression ["MUHJ6260452"]', ['MUHJ6260452'], [4, False]], ['partial-repair ["TSAZ4635083"]', ['TSAZ4635083'], [9, False]], ['partial-repair ["QSJZ1716340"]', ['QSJZ1716340'], [4, False]], ['control ["HRNU7843702"]', ['HRNU7843702'], [9, False]], ['control ["VGQU8532227"]', ['VGQU8532227'], [2, False]], ['control ["YQEU5793145"]', ['YQEU5793145'], [6, False]], ['control ["CTZU8384457"]', ['CTZU8384457'], [2, False]]], [['regression ["TRVJ4468592"]', ['TRVJ4468592'], [8, False]], ['regression ["VQAJ3159690"]', ['VQAJ3159690'], [0, True]], ['partial-repair ["ABCZ0000000"]', ['ABCZ0000000'], [5, False]], ['partial-repair ["TSAZ4635083"]', ['TSAZ4635083'], [9, False]], ['control ["FLAU0380833"]', ['FLAU0380833'], [7, False]], ['control ["OQHU9278051"]', ['OQHU9278051'], [8, False]], ['control ["LGSU0173454"]', ['LGSU0173454'], [8, False]], ['control ["RGOU0215685"]', ['RGOU0215685'], [3, False]]], [['regression ["QSJZ1716340"]', ['QSJZ1716340'], [4, False]], ['regression ["NACZ1755331"]', ['NACZ1755331'], [0, False]], ['partial-repair ["ABCZ0000000"]', ['ABCZ0000000'], [5, False]], ['control ["MJWU6668315"]', ['MJWU6668315'], [4, False]], ['control ["NPNU9965846"]', ['NPNU9965846'], [3, False]], ['control ["CCQU2344092"]', ['CCQU2344092'], [4, False]], ['control ["CSQU3054383"]', ['CSQU3054383'], [3, True]], ['control ["MSKU9070323"]', ['MSKU9070323'], [3, True]]], [['regression ["ABCZ0000000"]', ['ABCZ0000000'], [5, False]], ['regression ["XYZJ9999999"]', ['XYZJ9999999'], [1, False]], ['partial-repair ["QSJZ1716340"]', ['QSJZ1716340'], [4, False]], ['partial-repair ["NACZ1755331"]', ['NACZ1755331'], [0, False]], ['control ["TCLU1234560"]', ['TCLU1234560'], [8, False]], ['control ["CSQU305438"]', ['CSQU305438'], 'malformed'], ['control ["CSQX3054383"]', ['CSQX3054383'], 'malformed'], ['control ["csqu3054383"]', ['csqu3054383'], 'malformed']], [['regression ["MUHJ6260452"]', ['MUHJ6260452'], [4, False]], ['regression ["GEDJ3497886"]', ['GEDJ3497886'], [3, False]], ['partial-repair ["TSAZ4635083"]', ['TSAZ4635083'], [9, False]], ['partial-repair ["QSJZ1716340"]', ['QSJZ1716340'], [4, False]], ['control ["HRNU7843702"]', ['HRNU7843702'], [9, False]], ['control ["VGQU8532227"]', ['VGQU8532227'], [2, False]], ['control ["YQEU5793145"]', ['YQEU5793145'], [6, False]], ['control ["CTZU8384457"]', ['CTZU8384457'], [2, False]]]]
for label, args, expected in fixtures[N - 1]:
    check(label, 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
regression ["BYYJ6917585"]	`malformed`	`[8, False]`	Failed
regression ["MUHJ6260452"]	`malformed`	`[4, False]`	Failed
partial-repair ["TSAZ4635083"]	`malformed`	`[9, False]`	Failed
partial-repair ["QSJZ1716340"]	`malformed`	`[4, False]`	Failed
control ["HRNU7843702"]	`[9, False]`	`[9, False]`	Passed
control ["VGQU8532227"]	`[2, False]`	`[2, False]`	Passed
control ["YQEU5793145"]	`[6, False]`	`[6, False]`	Passed
control ["CTZU8384457"]	`[2, False]`	`[2, False]`	Passed

SHA-256 / 3b43ee85dcf6e1a10fb530fd7241a2901958e3a166528ca4180643fd47d99996

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(s):
    if len(s) != 11 or not s.isascii() or not s[:3].isalpha() or not s[:3].isupper():
        return 'malformed'
    if s[3] not in 'UJ' or not s[4:].isdigit():
        return 'malformed'
    vals = {}
    v = 10
    for ch in 'ABCDEFGHIJKLMNOPQRSTUVWXYZ':
        if v % 11 == 0:
            v += 1
        vals[ch] = v
        v += 1
    total = 0
    for i, ch in enumerate(s[:10]):
        total += (vals[ch] if ch.isalpha() else int(ch)) * 2 ** i
    check = total % 11 % 10
    return [check, check == int(s[10])]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression ["BYYJ6917585"]', ['BYYJ6917585'], [8, False]], ['regression ["MUHJ6260452"]', ['MUHJ6260452'], [4, False]], ['partial-repair ["TSAZ4635083"]', ['TSAZ4635083'], [9, False]], ['partial-repair ["QSJZ1716340"]', ['QSJZ1716340'], [4, False]], ['control ["HRNU7843702"]', ['HRNU7843702'], [9, False]], ['control ["VGQU8532227"]', ['VGQU8532227'], [2, False]], ['control ["YQEU5793145"]', ['YQEU5793145'], [6, False]], ['control ["CTZU8384457"]', ['CTZU8384457'], [2, False]]], [['regression ["TRVJ4468592"]', ['TRVJ4468592'], [8, False]], ['regression ["VQAJ3159690"]', ['VQAJ3159690'], [0, True]], ['partial-repair ["ABCZ0000000"]', ['ABCZ0000000'], [5, False]], ['partial-repair ["TSAZ4635083"]', ['TSAZ4635083'], [9, False]], ['control ["FLAU0380833"]', ['FLAU0380833'], [7, False]], ['control ["OQHU9278051"]', ['OQHU9278051'], [8, False]], ['control ["LGSU0173454"]', ['LGSU0173454'], [8, False]], ['control ["RGOU0215685"]', ['RGOU0215685'], [3, False]]], [['regression ["QSJZ1716340"]', ['QSJZ1716340'], [4, False]], ['regression ["NACZ1755331"]', ['NACZ1755331'], [0, False]], ['partial-repair ["ABCZ0000000"]', ['ABCZ0000000'], [5, False]], ['control ["MJWU6668315"]', ['MJWU6668315'], [4, False]], ['control ["NPNU9965846"]', ['NPNU9965846'], [3, False]], ['control ["CCQU2344092"]', ['CCQU2344092'], [4, False]], ['control ["CSQU3054383"]', ['CSQU3054383'], [3, True]], ['control ["MSKU9070323"]', ['MSKU9070323'], [3, True]]], [['regression ["ABCZ0000000"]', ['ABCZ0000000'], [5, False]], ['regression ["XYZJ9999999"]', ['XYZJ9999999'], [1, False]], ['partial-repair ["QSJZ1716340"]', ['QSJZ1716340'], [4, False]], ['partial-repair ["NACZ1755331"]', ['NACZ1755331'], [0, False]], ['control ["TCLU1234560"]', ['TCLU1234560'], [8, False]], ['control ["CSQU305438"]', ['CSQU305438'], 'malformed'], ['control ["CSQX3054383"]', ['CSQX3054383'], 'malformed'], ['control ["csqu3054383"]', ['csqu3054383'], 'malformed']], [['regression ["MUHJ6260452"]', ['MUHJ6260452'], [4, False]], ['regression ["GEDJ3497886"]', ['GEDJ3497886'], [3, False]], ['partial-repair ["TSAZ4635083"]', ['TSAZ4635083'], [9, False]], ['partial-repair ["QSJZ1716340"]', ['QSJZ1716340'], [4, False]], ['control ["HRNU7843702"]', ['HRNU7843702'], [9, False]], ['control ["VGQU8532227"]', ['VGQU8532227'], [2, False]], ['control ["YQEU5793145"]', ['YQEU5793145'], [6, False]], ['control ["CTZU8384457"]', ['CTZU8384457'], [2, False]]]]
for label, args, expected in fixtures[N - 1]:
    check(label, 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
regression ["BYYJ6917585"]	`[8, False]`	`[8, False]`	Passed
regression ["MUHJ6260452"]	`[4, False]`	`[4, False]`	Passed
partial-repair ["TSAZ4635083"]	`malformed`	`[9, False]`	Failed
partial-repair ["QSJZ1716340"]	`malformed`	`[4, False]`	Failed
control ["HRNU7843702"]	`[9, False]`	`[9, False]`	Passed
control ["VGQU8532227"]	`[2, False]`	`[2, False]`	Passed
control ["YQEU5793145"]	`[6, False]`	`[6, False]`	Passed
control ["CTZU8384457"]	`[2, False]`	`[2, False]`	Passed

SHA-256 / df0cdeab5170174995b73d2d4e1203397a76772653e28ba09dce12b81e37aacf

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(s):
    if len(s) != 11 or not s.isascii() or not s[:3].isalpha() or not s[:3].isupper():
        return 'malformed'
    if s[3] not in 'UJZ' or not s[4:].isdigit():
        return 'malformed'
    vals = {}
    v = 10
    for ch in 'ABCDEFGHIJKLMNOPQRSTUVWXYZ':
        if v % 11 == 0:
            v += 1
        vals[ch] = v
        v += 1
    total = 0
    for i, ch in enumerate(s[:10]):
        total += (vals[ch] if ch.isalpha() else int(ch)) * 2 ** i
    check = total % 11 % 10
    return [check, check == int(s[10])]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression ["BYYJ6917585"]', ['BYYJ6917585'], [8, False]], ['regression ["MUHJ6260452"]', ['MUHJ6260452'], [4, False]], ['partial-repair ["TSAZ4635083"]', ['TSAZ4635083'], [9, False]], ['partial-repair ["QSJZ1716340"]', ['QSJZ1716340'], [4, False]], ['control ["HRNU7843702"]', ['HRNU7843702'], [9, False]], ['control ["VGQU8532227"]', ['VGQU8532227'], [2, False]], ['control ["YQEU5793145"]', ['YQEU5793145'], [6, False]], ['control ["CTZU8384457"]', ['CTZU8384457'], [2, False]]], [['regression ["TRVJ4468592"]', ['TRVJ4468592'], [8, False]], ['regression ["VQAJ3159690"]', ['VQAJ3159690'], [0, True]], ['partial-repair ["ABCZ0000000"]', ['ABCZ0000000'], [5, False]], ['partial-repair ["TSAZ4635083"]', ['TSAZ4635083'], [9, False]], ['control ["FLAU0380833"]', ['FLAU0380833'], [7, False]], ['control ["OQHU9278051"]', ['OQHU9278051'], [8, False]], ['control ["LGSU0173454"]', ['LGSU0173454'], [8, False]], ['control ["RGOU0215685"]', ['RGOU0215685'], [3, False]]], [['regression ["QSJZ1716340"]', ['QSJZ1716340'], [4, False]], ['regression ["NACZ1755331"]', ['NACZ1755331'], [0, False]], ['partial-repair ["ABCZ0000000"]', ['ABCZ0000000'], [5, False]], ['control ["MJWU6668315"]', ['MJWU6668315'], [4, False]], ['control ["NPNU9965846"]', ['NPNU9965846'], [3, False]], ['control ["CCQU2344092"]', ['CCQU2344092'], [4, False]], ['control ["CSQU3054383"]', ['CSQU3054383'], [3, True]], ['control ["MSKU9070323"]', ['MSKU9070323'], [3, True]]], [['regression ["ABCZ0000000"]', ['ABCZ0000000'], [5, False]], ['regression ["XYZJ9999999"]', ['XYZJ9999999'], [1, False]], ['partial-repair ["QSJZ1716340"]', ['QSJZ1716340'], [4, False]], ['partial-repair ["NACZ1755331"]', ['NACZ1755331'], [0, False]], ['control ["TCLU1234560"]', ['TCLU1234560'], [8, False]], ['control ["CSQU305438"]', ['CSQU305438'], 'malformed'], ['control ["CSQX3054383"]', ['CSQX3054383'], 'malformed'], ['control ["csqu3054383"]', ['csqu3054383'], 'malformed']], [['regression ["MUHJ6260452"]', ['MUHJ6260452'], [4, False]], ['regression ["GEDJ3497886"]', ['GEDJ3497886'], [3, False]], ['partial-repair ["TSAZ4635083"]', ['TSAZ4635083'], [9, False]], ['partial-repair ["QSJZ1716340"]', ['QSJZ1716340'], [4, False]], ['control ["HRNU7843702"]', ['HRNU7843702'], [9, False]], ['control ["VGQU8532227"]', ['VGQU8532227'], [2, False]], ['control ["YQEU5793145"]', ['YQEU5793145'], [6, False]], ['control ["CTZU8384457"]', ['CTZU8384457'], [2, False]]]]
for label, args, expected in fixtures[N - 1]:
    check(label, 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
regression ["BYYJ6917585"]	`[8, False]`	`[8, False]`	Passed
regression ["MUHJ6260452"]	`[4, False]`	`[4, False]`	Passed
partial-repair ["TSAZ4635083"]	`[9, False]`	`[9, False]`	Passed
partial-repair ["QSJZ1716340"]	`[4, False]`	`[4, False]`	Passed
control ["HRNU7843702"]	`[9, False]`	`[9, False]`	Passed
control ["VGQU8532227"]	`[2, False]`	`[2, False]`	Passed
control ["YQEU5793145"]	`[6, False]`	`[6, False]`	Passed
control ["CTZU8384457"]	`[2, False]`	`[2, False]`	Passed

SHA-256 / 78d8c8108aa4ab362d6a2e940afb42b7271e52dd359578fe49636733b2ce422c

Verification & scope

A deterministic, bounded teaching model of the named scheme under the stated contract; not a certified validator. 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 2026-09-29T14:48:41.013326+00:00.

Case digest / 4ed48b6f85e2524247b9c8121e0017afb822494ea9c823625997b20e13664ba2