FA-3961 / Text processing / Open access

A replacement repeats until newly created matches disappear · case 01

A replacement repeats until newly created matches disappear.

Verified by executionVariant 1 · 4 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The implementation applies an operation whose text or grammar semantics violate this contract: Perform one left-to-right nonoverlapping replacement pass of aa to a.

VERIFIED REPAIR

Implement the complete stated contract, including the boundary fixtures: Perform one left-to-right nonoverlapping replacement pass of aa to a.

Unsuccessful approach: The attempted repair handles the primary example but still violates a separate boundary of the same contract.

Case contract

Perform one left-to-right nonoverlapping replacement pass of aa to a.

Why this case matters

A local executable model for consumers of structured text; oracle values are authored literals, not outputs copied from the repaired implementation.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return x.replace('aa','a').replace('aa','a')
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve('aaaa'), 'aa')
check('boundary 2', solve('aaa'), 'aa')
check('boundary 3', solve('aba'), 'aba')
check('boundary 4', solve(''), '')
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
boundary 1	`a`	`aa`	Failed
boundary 2	`a`	`aa`	Failed
boundary 3	`aba`	`aba`	Passed
boundary 4			Passed

SHA-256 / a9f207eb59a211deee671445d520563dad4d9367243c51d8f4e568c60d40653d

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return re.sub('a+','a',x)
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve('aaaa'), 'aa')
check('boundary 2', solve('aaa'), 'aa')
check('boundary 3', solve('aba'), 'aba')
check('boundary 4', solve(''), '')
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
boundary 1	`a`	`aa`	Failed
boundary 2	`a`	`aa`	Failed
boundary 3	`aba`	`aba`	Passed
boundary 4			Passed

SHA-256 / e839d97eb8a67ed30a3979055fc55e95a670dc9fd9ee407e2800732a399fb43d

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return x.replace('aa','a')
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve('aaaa'), 'aa')
check('boundary 2', solve('aaa'), 'aa')
check('boundary 3', solve('aba'), 'aba')
check('boundary 4', solve(''), '')
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
boundary 1	`aa`	`aa`	Passed
boundary 2	`aa`	`aa`	Passed
boundary 3	`aba`	`aba`	Passed
boundary 4			Passed

SHA-256 / 9b4c316fa6973c8a367fe492627546e8cf26b024181ad1bcf9cb0f26443ead27

Verification & scope

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 2026-09-29T14:37:33.569483+00:00.

Case digest / 30ecb2ee0cafb1acd3d84abd8aa365cdff4e97cbdc16f86bff80310603226507