FA-79346 / Barcode symbology encoding / Open access

EAN-13 parity rows for leading digits 7 and 8 are exchanged · case 01

Codes starting with 7 decode as starting with 8 and vice versa, silently changing the country prefix.

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

ROOT CAUSE

The parity table lists the rows for 7 and 8 in swapped order.

THE FAILURE

The parity table lists the rows for 7 and 8 in swapped order.

Unsuccessful approach: Duplicating the 7 row makes 8-prefixed codes decode as 7.

Case contract

Encode a 13-character string of ASCII digits (the check digit is taken as given, not verified) as the 95-module EAN-13 pattern: start guard 101, six left digits in L or G sets chosen by the parity row of the leading digit, centre guard 01010, six right digits in the R set, end guard 101. R is the bitwise complement of L and G is R reversed. Anything else 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(code):
    if len(code) != 13 or not all(ch in '0123456789' for ch in code):
        return None
    L = ['0001101', '0011001', '0010011', '0111101', '0100011', '0110001', '0101111', '0111011', '0110111', '0001011']
    R = [''.join('1' if b == '0' else '0' for b in p) for p in L]
    G = [p[::-1] for p in R]
    parity = ['LLLLLL', 'LLGLGG', 'LLGGLG', 'LLGGGL', 'LGLLGG', 'LGGLLG', 'LGGGLL', 'LGLGGL', 'LGLGLG', 'LGGLGL']
    pat = parity[int(code[0])]
    left = ''.join((L if pat[i] == 'L' else G)[int(code[1 + i])] for i in range(6))
    right = ''.join(R[int(ch)] for ch in code[7:])
    return '101' + left + '01010' + right + '101'
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['8708854500750', '10101110110100111011011100010010111001010001101010100111011100101110010100010010011101110010101'], ['8966493447779', '10100010110000101010111100111010010111011110101010101110010111001000100100010010001001110100101'], ['5569719879594', '10101100010000101001011101110110011001001011101010100100010001001110100100111011101001011100101'], ['5564657964331', '10101100010000101001110101011110110001001000101010111010010100001011100100001010000101100110101'], ['3339552094472', '10101111010111101001011101110010111001001001101010111001011101001011100101110010001001101100101'], ['2923603435282', '10100010110010011010000100001010001101010000101010101110010000101001110110110010010001101100101'], ['3510413208309', '10101100010011001010011100111010110011011110101010110110011100101001000100001011100101110100101'], ['8535822111223', '10101100010100001011000100010010011011001001101010110011011001101100110110110011011001000010101']], [['8021320736862', '10100011010011011001100101000010011011000110101010100010010000101010000100100010100001101100101'], ['8355706274976', '10101111010111001011000100100010100111010111101010110110010001001011100111010010001001010000101'], ['0777861705172', '10101110110111011011101101101110101111001100101010100010011100101001110110011010001001101100101'], ['6141838617595', '10100110010011101011001100010010111101011011101010101000011001101000100100111011101001001110101'], ['3766842531699', '10101110110101111000010100010010011101001001101010100111010000101100110101000011101001110100101'], ['5117058572420', '10100110010110011001000100011010110001000100101010100111010001001101100101110011011001110010101'], ['4641860725337', '10101011110011101001100101101110000101010011101010100010011011001001110100001010000101000100101'], ['7358317090517', '10101111010111001011011101000010011001001000101010111001011101001110010100111011001101000100101']], [['7867470575448', '10101101110000101011101100111010111011010011101010100111010001001001110101110010111001001000101'], ['8763496138721', '10101110110000101011110100111010010111010111101010110011010000101001000100010011011001100110101'], ['8457347577022', '10101000110111001011101101000010011101011101101010100111010001001000100111001011011001101100101'], ['3716511088176', '10101110110011001000010101110010110011001100101010111001010010001001000110011010001001010000101'], ['5108124299029', '10100110010100111000100100110010010011001110101010110110011101001110100111001011011001110100101'], ['4275982832382', '10100100110010001011000100010110001001001101101010100100010000101101100100001010010001101100101'], ['1841559138266', '10101101110100011011001101100010111001001011101010110011010000101001000110110010100001010000101'], ['7062168881750', '10100011010000101001001101100110101111000100101010100100010010001100110100010010011101110010101']], [['8352800374001', '10101111010111001001001100010010100111000110101010100001010001001011100111001011100101100110101'], ['8557236078630', '10101100010111001011101100110110100001010111101010111001010001001001000101000010000101110010101'], ['1986892142891', '10100010110110111000010101101110010111001101101010110011010111001101100100100011101001100110101'], ['6087726577121', '10100011010001001001000100100010010011010111101010100111010001001000100110011011011001100110101'], ['9139450687171', '10100110010100001001011101000110111001000110101010101000010010001000100110011010001001100110101'], ['9147502050346', '10100110010011101001000101100010100111001001101010111001010011101110010100001010111001010000101'], ['3621226624482', '10101011110010011011001100110110011011010111101010101000011011001011100101110010010001101100101'], ['8651558989874', '10101011110111001001100101110010111001011011101010111010010010001110100100100010001001011100101']], [['7195448424184', '10100110010010111011000100111010100011000100101010101110011011001011100110011010010001011100101'], ['8606108755061', '10101011110100111010111101100110100111011011101010100010010011101001110111001010100001100110101'], ['8930890112346', '10100010110100001000110100010010010111000110101010110011011001101101100100001010111001010000101'], ['9803396505759', '10101101110100111010000101111010010111010111101010100111011100101001110100010010011101110100101'], ['5845180047269', '10101101110011101011100100110010110111010011101010111001010111001000100110110010100001110100101'], ['9648988190302', '10101011110011101000100100010110001001011011101010110011011101001110010100001011100101101100101'], ['2139834231886', '10100110010111101001011100010010111101001110101010110110010000101100110100100010010001010000101'], ['8011609402200', '10100011010110011001100100001010100111000101101010101110011100101101100110110011100101110010101']]]
labels = ["regression: parity rows for leading 7 and 8", "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: parity rows for leading 7 and 8 0	`10101110110100111011011100010010110001001110101010100111011100101110010100010010011101110010101`	`10101110110100111011011100010010111001010001101010100111011100101110010100010010011101110010101`	Failed
repair trap 1	`10100010110000101010111100111010001011010000101010101110010111001000100100010010001001110100101`	`10100010110000101010111100111010010111011110101010101110010111001000100100010010001001110100101`	Failed
combined fault 2	`10101100010000101001011101110110011001001011101010100100010001001110100100111011101001011100101`	`10101100010000101001011101110110011001001011101010100100010001001110100100111011101001011100101`	Passed
control 3	`10101100010000101001110101011110110001001000101010111010010100001011100100001010000101100110101`	`10101100010000101001110101011110110001001000101010111010010100001011100100001010000101100110101`	Passed
control 4	`10101111010111101001011101110010111001001001101010111001011101001011100101110010001001101100101`	`10101111010111101001011101110010111001001001101010111001011101001011100101110010001001101100101`	Passed
boundary 5	`10100010110010011010000100001010001101010000101010101110010000101001110110110010010001101100101`	`10100010110010011010000100001010001101010000101010101110010000101001110110110010010001101100101`	Passed
boundary 6	`10101100010011001010011100111010110011011110101010110110011100101001000100001011100101110100101`	`10101100010011001010011100111010110011011110101010110110011100101001000100001011100101110100101`	Passed
control 7	`10101100010100001011000100010010010011001101101010110011011001101100110110110011011001000010101`	`10101100010100001011000100010010011011001001101010110011011001101100110110110011011001000010101`	Failed

SHA-256 / 7896321ef75064a10f82b2521f80b1a9fd081b5f24cd4bff061f96ca22cc37f9

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(code):
    if len(code) != 13 or not all(ch in '0123456789' for ch in code):
        return None
    L = ['0001101', '0011001', '0010011', '0111101', '0100011', '0110001', '0101111', '0111011', '0110111', '0001011']
    R = [''.join('1' if b == '0' else '0' for b in p) for p in L]
    G = [p[::-1] for p in R]
    parity = ['LLLLLL', 'LLGLGG', 'LLGGLG', 'LLGGGL', 'LGLLGG', 'LGGLLG', 'LGGGLL', 'LGLGLG', 'LGLGLG', 'LGGLGL']
    pat = parity[int(code[0])]
    left = ''.join((L if pat[i] == 'L' else G)[int(code[1 + i])] for i in range(6))
    right = ''.join(R[int(ch)] for ch in code[7:])
    return '101' + left + '01010' + right + '101'
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['8708854500750', '10101110110100111011011100010010111001010001101010100111011100101110010100010010011101110010101'], ['8966493447779', '10100010110000101010111100111010010111011110101010101110010111001000100100010010001001110100101'], ['5569719879594', '10101100010000101001011101110110011001001011101010100100010001001110100100111011101001011100101'], ['5564657964331', '10101100010000101001110101011110110001001000101010111010010100001011100100001010000101100110101'], ['3339552094472', '10101111010111101001011101110010111001001001101010111001011101001011100101110010001001101100101'], ['2923603435282', '10100010110010011010000100001010001101010000101010101110010000101001110110110010010001101100101'], ['3510413208309', '10101100010011001010011100111010110011011110101010110110011100101001000100001011100101110100101'], ['8535822111223', '10101100010100001011000100010010011011001001101010110011011001101100110110110011011001000010101']], [['8021320736862', '10100011010011011001100101000010011011000110101010100010010000101010000100100010100001101100101'], ['8355706274976', '10101111010111001011000100100010100111010111101010110110010001001011100111010010001001010000101'], ['0777861705172', '10101110110111011011101101101110101111001100101010100010011100101001110110011010001001101100101'], ['6141838617595', '10100110010011101011001100010010111101011011101010101000011001101000100100111011101001001110101'], ['3766842531699', '10101110110101111000010100010010011101001001101010100111010000101100110101000011101001110100101'], ['5117058572420', '10100110010110011001000100011010110001000100101010100111010001001101100101110011011001110010101'], ['4641860725337', '10101011110011101001100101101110000101010011101010100010011011001001110100001010000101000100101'], ['7358317090517', '10101111010111001011011101000010011001001000101010111001011101001110010100111011001101000100101']], [['7867470575448', '10101101110000101011101100111010111011010011101010100111010001001001110101110010111001001000101'], ['8763496138721', '10101110110000101011110100111010010111010111101010110011010000101001000100010011011001100110101'], ['8457347577022', '10101000110111001011101101000010011101011101101010100111010001001000100111001011011001101100101'], ['3716511088176', '10101110110011001000010101110010110011001100101010111001010010001001000110011010001001010000101'], ['5108124299029', '10100110010100111000100100110010010011001110101010110110011101001110100111001011011001110100101'], ['4275982832382', '10100100110010001011000100010110001001001101101010100100010000101101100100001010010001101100101'], ['1841559138266', '10101101110100011011001101100010111001001011101010110011010000101001000110110010100001010000101'], ['7062168881750', '10100011010000101001001101100110101111000100101010100100010010001100110100010010011101110010101']], [['8352800374001', '10101111010111001001001100010010100111000110101010100001010001001011100111001011100101100110101'], ['8557236078630', '10101100010111001011101100110110100001010111101010111001010001001001000101000010000101110010101'], ['1986892142891', '10100010110110111000010101101110010111001101101010110011010111001101100100100011101001100110101'], ['6087726577121', '10100011010001001001000100100010010011010111101010100111010001001000100110011011011001100110101'], ['9139450687171', '10100110010100001001011101000110111001000110101010101000010010001000100110011010001001100110101'], ['9147502050346', '10100110010011101001000101100010100111001001101010111001010011101110010100001010111001010000101'], ['3621226624482', '10101011110010011011001100110110011011010111101010101000011011001011100101110010010001101100101'], ['8651558989874', '10101011110111001001100101110010111001011011101010111010010010001110100100100010001001011100101']], [['7195448424184', '10100110010010111011000100111010100011000100101010101110011011001011100110011010010001011100101'], ['8606108755061', '10101011110100111010111101100110100111011011101010100010010011101001110111001010100001100110101'], ['8930890112346', '10100010110100001000110100010010010111000110101010110011011001101101100100001010111001010000101'], ['9803396505759', '10101101110100111010000101111010010111010111101010100111011100101001110100010010011101110100101'], ['5845180047269', '10101101110011101011100100110010110111010011101010111001010111001000100110110010100001110100101'], ['9648988190302', '10101011110011101000100100010110001001011011101010110011011101001110010100001011100101101100101'], ['2139834231886', '10100110010111101001011100010010111101001110101010110110010000101100110100100010010001010000101'], ['8011609402200', '10100011010110011001100100001010100111000101101010101110011100101101100110110011100101110010101']]]
labels = ["regression: parity rows for leading 7 and 8", "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: parity rows for leading 7 and 8 0	`10101110110100111011011100010010110001001110101010100111011100101110010100010010011101110010101`	`10101110110100111011011100010010111001010001101010100111011100101110010100010010011101110010101`	Failed
repair trap 1	`10100010110000101010111100111010001011010000101010101110010111001000100100010010001001110100101`	`10100010110000101010111100111010010111011110101010101110010111001000100100010010001001110100101`	Failed
combined fault 2	`10101100010000101001011101110110011001001011101010100100010001001110100100111011101001011100101`	`10101100010000101001011101110110011001001011101010100100010001001110100100111011101001011100101`	Passed
control 3	`10101100010000101001110101011110110001001000101010111010010100001011100100001010000101100110101`	`10101100010000101001110101011110110001001000101010111010010100001011100100001010000101100110101`	Passed
control 4	`10101111010111101001011101110010111001001001101010111001011101001011100101110010001001101100101`	`10101111010111101001011101110010111001001001101010111001011101001011100101110010001001101100101`	Passed
boundary 5	`10100010110010011010000100001010001101010000101010101110010000101001110110110010010001101100101`	`10100010110010011010000100001010001101010000101010101110010000101001110110110010010001101100101`	Passed
boundary 6	`10101100010011001010011100111010110011011110101010110110011100101001000100001011100101110100101`	`10101100010011001010011100111010110011011110101010110110011100101001000100001011100101110100101`	Passed
control 7	`10101100010100001011000100010010010011001101101010110011011001101100110110110011011001000010101`	`10101100010100001011000100010010011011001001101010110011011001101100110110110011011001000010101`	Failed

SHA-256 / f750d5812b8555e0c83d8f4955dd227e88c551f93ca8377f28e0a6ed5e503f7e

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 2026-09-29T14:49:43.758492+00:00.

Case digest / d5239778c9fef114a34e552e434d298ac24f08434a4f93a1a89a308864ea97ea