FA-79516 / Barcode symbology encoding / Open access

ITF puts the second digit of each pair in the bars · case 01

Every digit pair scans reversed, so 1234 reads as 2143.

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

ROOT CAUSE

Bars take the second digit's pattern and spaces the first.

THE FAILURE

Bars take the second digit's pattern and spaces the first.

Unsuccessful approach: Reading the space pattern backwards corrupts the second digit.

Case contract

Encode ASCII digits as Interleaved 2 of 5 element widths (narrow 1, wide = ratio in {2, 2.5, 3}). An odd-length input gets a leading 0. Start is narrow bar/space/bar/space; each digit pair interleaves the first digit's pattern in the bars with the second digit's pattern in the spaces; stop is wide bar, narrow space, narrow bar. Digit patterns use weights 1,2,4,7 plus parity (0 = NNWWN). Invalid input returns None.

Why this case matters

Retail, logistics, pharmacy and document workflows depend on encoders that produce exactly the module pattern, code-set switches, separators and quiet zones scanners expect; one misplaced module or separator makes a label unreadable or, worse, scan as different data.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(digits, ratio):
    if not digits or not all(c in '0123456789' for c in digits) or ratio not in (2, 2.5, 3):
        return None
    P = {'0': 'NNWWN', '1': 'WNNNW', '2': 'NWNNW', '3': 'WWNNN', '4': 'NNWNW',
         '5': 'WNWNN', '6': 'NWWNN', '7': 'NNNWW', '8': 'WNNWN', '9': 'NWNWN'}
    if len(digits) % 2:
        digits = '0' + digits
    wid = {'N': 1, 'W': ratio}
    out = [1, 1, 1, 1]
    for i in range(0, len(digits), 2):
        a, b = P[digits[i]], P[digits[i + 1]]
        for k in range(5):
            out.append(wid[b[k]])
            out.append(wid[a[k]])
    out += [ratio, 1, 1]
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[('809220', 3), [1, 1, 1, 1, 3, 1, 1, 1, 1, 3, 3, 3, 1, 1, 1, 1, 3, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 3, 3, 1, 3, 1, 1]], [('2', 2.5), [1, 1, 1, 1, 1, 1, 1, 2.5, 2.5, 1, 2.5, 1, 1, 2.5, 2.5, 1, 1]], [('596257', 4), None], [('37775', 4), None], [('683', 4), None], [('395208', 4), None], [('4528', 4), None], [('960081', 3), [1, 1, 1, 1, 1, 1, 3, 3, 1, 3, 3, 1, 1, 1, 1, 1, 1, 1, 3, 3, 3, 3, 1, 1, 3, 3, 1, 1, 1, 1, 3, 1, 1, 3, 3, 1, 1]]], [[('954', 3), [1, 1, 1, 1, 1, 1, 1, 3, 3, 1, 3, 3, 1, 1, 3, 1, 1, 1, 3, 3, 1, 1, 1, 3, 3, 1, 1]], [('246919', 2), [1, 1, 1, 1, 1, 1, 2, 1, 1, 2, 1, 1, 2, 2, 1, 1, 2, 2, 2, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 1, 2, 2, 1, 2, 1, 1]], [('13', 4), None], [('296045', 4), None], [('402165', 4), None], [('044955', 4), None], [('803415', 4), None], [('5377', 2), [1, 1, 1, 1, 2, 2, 1, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 1, 1]]], [[('486862', 3), [1, 1, 1, 1, 1, 3, 1, 1, 3, 1, 1, 3, 3, 1, 1, 3, 3, 1, 3, 1, 1, 3, 1, 1, 1, 1, 3, 3, 3, 1, 1, 1, 1, 3, 3, 1, 1]], [('05', 2), [1, 1, 1, 1, 1, 2, 1, 1, 2, 2, 2, 1, 1, 1, 2, 1, 1]], [('820280', 4), None], [('5694', 4), None], [('977', 4), None], [('80', 4), None], [('159055', 4), None], [('15', 3), [1, 1, 1, 1, 3, 3, 1, 1, 1, 3, 1, 1, 3, 1, 3, 1, 1]]], [[('6298', 3), [1, 1, 1, 1, 1, 1, 3, 3, 3, 1, 1, 1, 1, 3, 1, 3, 3, 1, 1, 1, 3, 3, 1, 1, 3, 1, 1]], [('74', 2.5), [1, 1, 1, 1, 1, 1, 1, 1, 1, 2.5, 2.5, 1, 2.5, 2.5, 2.5, 1, 1]], [('00', 4), None], [('909384', 4), None], [('4', 4), None], [('72', 4), None], [('69867', 4), None], [('17', 3), [1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 3, 3, 3, 3, 1, 1]]], [[('48', 3), [1, 1, 1, 1, 1, 3, 1, 1, 3, 1, 1, 3, 3, 1, 3, 1, 1]], [('151516', 2.5), [1, 1, 1, 1, 2.5, 2.5, 1, 1, 1, 2.5, 1, 1, 2.5, 1, 2.5, 2.5, 1, 1, 1, 2.5, 1, 1, 2.5, 1, 2.5, 1, 1, 2.5, 1, 2.5, 1, 1, 2.5, 1, 2.5, 1, 1]], [('6', 4), None], [('2527', 4), None], [('156', 4), None], [('8', 4), None], [('460', 4), None], [('420', 3), [1, 1, 1, 1, 1, 1, 1, 1, 3, 3, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 3, 3, 1, 3, 1, 1]]]]
labels = ["regression: bar and space interleaving", "repair trap", "combined fault", "control", "control", "boundary", "boundary", "control"]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("%s %d" % (labels[i % len(labels)], 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
regression: bar and space interleaving 0	`[1, 1, 1, 1, 1, 3, 1, 1, 3, 1, 3, 3, 1, 1, 1, 1, 3, 3, 1, 1, 1, 3, 3, 1, 1, 1, 1, 3, 3, 1, 3, 1, 1, 3, 3, 1, 1]`	`[1, 1, 1, 1, 3, 1, 1, 1, 1, 3, 3, 3, 1, 1, 1, 1, 3, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 3, 3, 1, 3, 1, 1]`	Failed
repair trap 1	`[1, 1, 1, 1, 1, 1, 2.5, 1, 1, 2.5, 1, 2.5, 2.5, 1, 2.5, 1, 1]`	`[1, 1, 1, 1, 1, 1, 1, 2.5, 2.5, 1, 2.5, 1, 1, 2.5, 2.5, 1, 1]`	Failed
combined fault 2	`None`	`None`	Passed
control 3	`None`	`None`	Passed
control 4	`None`	`None`	Passed
boundary 5	`None`	`None`	Passed
boundary 6	`None`	`None`	Passed
control 7	`[1, 1, 1, 1, 1, 1, 3, 3, 3, 1, 1, 3, 1, 1, 1, 1, 1, 1, 3, 3, 3, 3, 1, 1, 3, 3, 1, 1, 1, 1, 1, 3, 3, 1, 3, 1, 1]`	`[1, 1, 1, 1, 1, 1, 3, 3, 1, 3, 3, 1, 1, 1, 1, 1, 1, 1, 3, 3, 3, 3, 1, 1, 3, 3, 1, 1, 1, 1, 3, 1, 1, 3, 3, 1, 1]`	Failed

SHA-256 / 7bc4731f47c33e2d131f6cf9a0e9bd1151b0cd759ac4011298ea8cf6c5544ad7

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(digits, ratio):
    if not digits or not all(c in '0123456789' for c in digits) or ratio not in (2, 2.5, 3):
        return None
    P = {'0': 'NNWWN', '1': 'WNNNW', '2': 'NWNNW', '3': 'WWNNN', '4': 'NNWNW',
         '5': 'WNWNN', '6': 'NWWNN', '7': 'NNNWW', '8': 'WNNWN', '9': 'NWNWN'}
    if len(digits) % 2:
        digits = '0' + digits
    wid = {'N': 1, 'W': ratio}
    out = [1, 1, 1, 1]
    for i in range(0, len(digits), 2):
        a, b = P[digits[i]], P[digits[i + 1]]
        for k in range(5):
            out.append(wid[a[k]])
            out.append(wid[b[4 - k]])
    out += [ratio, 1, 1]
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[('809220', 3), [1, 1, 1, 1, 3, 1, 1, 1, 1, 3, 3, 3, 1, 1, 1, 1, 3, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 3, 3, 1, 3, 1, 1]], [('2', 2.5), [1, 1, 1, 1, 1, 1, 1, 2.5, 2.5, 1, 2.5, 1, 1, 2.5, 2.5, 1, 1]], [('596257', 4), None], [('37775', 4), None], [('683', 4), None], [('395208', 4), None], [('4528', 4), None], [('960081', 3), [1, 1, 1, 1, 1, 1, 3, 3, 1, 3, 3, 1, 1, 1, 1, 1, 1, 1, 3, 3, 3, 3, 1, 1, 3, 3, 1, 1, 1, 1, 3, 1, 1, 3, 3, 1, 1]]], [[('954', 3), [1, 1, 1, 1, 1, 1, 1, 3, 3, 1, 3, 3, 1, 1, 3, 1, 1, 1, 3, 3, 1, 1, 1, 3, 3, 1, 1]], [('246919', 2), [1, 1, 1, 1, 1, 1, 2, 1, 1, 2, 1, 1, 2, 2, 1, 1, 2, 2, 2, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 1, 2, 2, 1, 2, 1, 1]], [('13', 4), None], [('296045', 4), None], [('402165', 4), None], [('044955', 4), None], [('803415', 4), None], [('5377', 2), [1, 1, 1, 1, 2, 2, 1, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 1, 1]]], [[('486862', 3), [1, 1, 1, 1, 1, 3, 1, 1, 3, 1, 1, 3, 3, 1, 1, 3, 3, 1, 3, 1, 1, 3, 1, 1, 1, 1, 3, 3, 3, 1, 1, 1, 1, 3, 3, 1, 1]], [('05', 2), [1, 1, 1, 1, 1, 2, 1, 1, 2, 2, 2, 1, 1, 1, 2, 1, 1]], [('820280', 4), None], [('5694', 4), None], [('977', 4), None], [('80', 4), None], [('159055', 4), None], [('15', 3), [1, 1, 1, 1, 3, 3, 1, 1, 1, 3, 1, 1, 3, 1, 3, 1, 1]]], [[('6298', 3), [1, 1, 1, 1, 1, 1, 3, 3, 3, 1, 1, 1, 1, 3, 1, 3, 3, 1, 1, 1, 3, 3, 1, 1, 3, 1, 1]], [('74', 2.5), [1, 1, 1, 1, 1, 1, 1, 1, 1, 2.5, 2.5, 1, 2.5, 2.5, 2.5, 1, 1]], [('00', 4), None], [('909384', 4), None], [('4', 4), None], [('72', 4), None], [('69867', 4), None], [('17', 3), [1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1, 3, 3, 3, 3, 1, 1]]], [[('48', 3), [1, 1, 1, 1, 1, 3, 1, 1, 3, 1, 1, 3, 3, 1, 3, 1, 1]], [('151516', 2.5), [1, 1, 1, 1, 2.5, 2.5, 1, 1, 1, 2.5, 1, 1, 2.5, 1, 2.5, 2.5, 1, 1, 1, 2.5, 1, 1, 2.5, 1, 2.5, 1, 1, 2.5, 1, 2.5, 1, 1, 2.5, 1, 2.5, 1, 1]], [('6', 4), None], [('2527', 4), None], [('156', 4), None], [('8', 4), None], [('460', 4), None], [('420', 3), [1, 1, 1, 1, 1, 1, 1, 1, 3, 3, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 3, 3, 1, 3, 1, 1]]]]
labels = ["regression: bar and space interleaving", "repair trap", "combined fault", "control", "control", "boundary", "boundary", "control"]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("%s %d" % (labels[i % len(labels)], 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
regression: bar and space interleaving 0	`[1, 1, 1, 1, 3, 1, 1, 3, 1, 3, 3, 1, 1, 1, 1, 3, 3, 1, 1, 1, 3, 3, 1, 1, 1, 1, 3, 3, 1, 3, 1, 1, 3, 1, 3, 1, 1]`	`[1, 1, 1, 1, 3, 1, 1, 1, 1, 3, 3, 3, 1, 1, 1, 1, 3, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 1, 3, 1, 3, 3, 1, 3, 1, 1]`	Failed
repair trap 1	`[1, 1, 1, 1, 1, 2.5, 1, 1, 2.5, 1, 2.5, 2.5, 1, 1, 2.5, 1, 1]`	`[1, 1, 1, 1, 1, 1, 1, 2.5, 2.5, 1, 2.5, 1, 1, 2.5, 2.5, 1, 1]`	Failed
combined fault 2	`None`	`None`	Passed
control 3	`None`	`None`	Passed
control 4	`None`	`None`	Passed
boundary 5	`None`	`None`	Passed
boundary 6	`None`	`None`	Passed
control 7	`[1, 1, 1, 1, 1, 1, 3, 1, 1, 3, 3, 3, 1, 1, 1, 1, 1, 3, 3, 3, 3, 1, 1, 1, 3, 3, 1, 1, 1, 1, 3, 1, 1, 3, 3, 1, 1]`	`[1, 1, 1, 1, 1, 1, 3, 3, 1, 3, 3, 1, 1, 1, 1, 1, 1, 1, 3, 3, 3, 3, 1, 1, 3, 3, 1, 1, 1, 1, 3, 1, 1, 3, 3, 1, 1]`	Failed

SHA-256 / f99ac391f2b1f4a1eefd81fdd8d517094230ddd7568599fb9fa02201283f38c5

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.

Member access is invitation-based. Sign in with your invited account to inspect the repair.

Verification & scope

A deterministic bounded teaching model with a stipulated contract; it makes no claim of conformance to any published specification. 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 2026-09-29T14:49:45.119868+00:00.

Case digest / 6c2224fab7c50e118dd7c010b2ff64f0981b0909c90134938275c5f53446ab66