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FA-47001 / Bounded deques / Open access

Lazy reversed deque appends at the wrong physical endpoint · case 01

Lazy reversed deque appends at the wrong physical endpoint.

Verified by executionVariant 1 · 9 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Lazy reversed deque appends at the wrong physical endpoint.

THE FAILURE

Lazy reversed deque appends at the wrong physical endpoint.

Unsuccessful approach: The partial repair still applies the incorrect transition to an admitted boundary or multi-element case.

Case contract

A bounded deque stores physical values and a lazy reversed flag. Flip toggles orientation without moving storage; logical append and front-pop select the appropriate physical endpoint. Full append rejects.

Why this case matters

Controlled bounded deque implementation model with explicit storage and lifecycle observations.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    storage,reverse,op,value,cap=x
    logical=storage[::-1] if reverse else storage[:]
    if op=='flip':return [storage,not reverse,logical[::-1],None]
    if op=='push':
        if len(storage)==cap:return [storage,reverse,logical,'full']
        physical=storage+[value]
        return [physical,reverse,logical+[value],None]
    if not storage:return [storage,reverse,logical,'empty']
    result=storage[:-1] if reverse else storage[1:]
    removed=storage[-1] if reverse else storage[0]
    remaining=result[::-1] if reverse else result[:]
    return [result,reverse,remaining,removed]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([[N,N+1,N+2],True,"pop",0,4]), {1: [[1, 2], True, [2, 1], 3], 2: [[2, 3], True, [3, 2], 4], 3: [[3, 4], True, [4, 3], 5], 4: [[4, 5], True, [5, 4], 6], 5: [[5, 6], True, [6, 5], 7]}[N])
check('1', solve([[N,N+1],True,"push",N+2,4]), {1: [[3, 1, 2], True, [2, 1, 3], None], 2: [[4, 2, 3], True, [3, 2, 4], None], 3: [[5, 3, 4], True, [4, 3, 5], None], 4: [[6, 4, 5], True, [5, 4, 6], None], 5: [[7, 5, 6], True, [6, 5, 7], None]}[N])
check('2', solve([[N,N+1],False,"flip",0,3]), {1: [[1, 2], True, [2, 1], None], 2: [[2, 3], True, [3, 2], None], 3: [[3, 4], True, [4, 3], None], 4: [[4, 5], True, [5, 4], None], 5: [[5, 6], True, [6, 5], None]}[N])
check('3', solve([[N,N+1],True,"flip",0,3]), {1: [[1, 2], False, [1, 2], None], 2: [[2, 3], False, [2, 3], None], 3: [[3, 4], False, [3, 4], None], 4: [[4, 5], False, [4, 5], None], 5: [[5, 6], False, [5, 6], None]}[N])
check('4', solve([[N],False,"push",N+1,1]), {1: [[1], False, [1], 'full'], 2: [[2], False, [2], 'full'], 3: [[3], False, [3], 'full'], 4: [[4], False, [4], 'full'], 5: [[5], False, [5], 'full']}[N])
check('5', solve([[],True,"pop",0,3]), {1: [[], True, [], 'empty'], 2: [[], True, [], 'empty'], 3: [[], True, [], 'empty'], 4: [[], True, [], 'empty'], 5: [[], True, [], 'empty']}[N])
check('6', solve([[N,N+1],False,"pop",0,3]), {1: [[2], False, [2], 1], 2: [[3], False, [3], 2], 3: [[4], False, [4], 3], 4: [[5], False, [5], 4], 5: [[6], False, [6], 5]}[N])
check('7', solve([[N],False,"push",N+1,3]), {1: [[1, 2], False, [1, 2], None], 2: [[2, 3], False, [2, 3], None], 3: [[3, 4], False, [3, 4], None], 4: [[4, 5], False, [4, 5], None], 5: [[5, 6], False, [5, 6], None]}[N])
check('full reversed rejection', solve([[N,N+1],True,'push',N+2,2]), [[N,N+1],True,[N+1,N],'full'])
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 fixtureActualExpectedOutcome
0[[1, 2], True, [2, 1], 3][[1, 2], True, [2, 1], 3]Passed
1[[1, 2, 3], True, [2, 1, 3], None][[3, 1, 2], True, [2, 1, 3], None]Failed
2[[1, 2], True, [2, 1], None][[1, 2], True, [2, 1], None]Passed
3[[1, 2], False, [1, 2], None][[1, 2], False, [1, 2], None]Passed
4[[1], False, [1], 'full'][[1], False, [1], 'full']Passed
5[[], True, [], 'empty'][[], True, [], 'empty']Passed
6[[2], False, [2], 1][[2], False, [2], 1]Passed
7[[1, 2], False, [1, 2], None][[1, 2], False, [1, 2], None]Passed
full reversed rejection[[1, 2], True, [2, 1], 'full'][[1, 2], True, [2, 1], 'full']Passed

SHA-256 / dee394027473e495d44ba739cd44bdcf9fc7b962c56046e22cb8b1c055ed5ded

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    storage,reverse,op,value,cap=x
    logical=storage[::-1] if reverse else storage[:]
    if op=='flip':return [storage,not reverse,logical[::-1],None]
    if op=='push':
        if len(storage)==cap:return [storage,reverse,logical,'full']
        physical=[value]+storage if reverse and len(storage)<2 else storage+[value]
        return [physical,reverse,logical+[value],None]
    if not storage:return [storage,reverse,logical,'empty']
    result=storage[:-1] if reverse else storage[1:]
    removed=storage[-1] if reverse else storage[0]
    remaining=result[::-1] if reverse else result[:]
    return [result,reverse,remaining,removed]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([[N,N+1,N+2],True,"pop",0,4]), {1: [[1, 2], True, [2, 1], 3], 2: [[2, 3], True, [3, 2], 4], 3: [[3, 4], True, [4, 3], 5], 4: [[4, 5], True, [5, 4], 6], 5: [[5, 6], True, [6, 5], 7]}[N])
check('1', solve([[N,N+1],True,"push",N+2,4]), {1: [[3, 1, 2], True, [2, 1, 3], None], 2: [[4, 2, 3], True, [3, 2, 4], None], 3: [[5, 3, 4], True, [4, 3, 5], None], 4: [[6, 4, 5], True, [5, 4, 6], None], 5: [[7, 5, 6], True, [6, 5, 7], None]}[N])
check('2', solve([[N,N+1],False,"flip",0,3]), {1: [[1, 2], True, [2, 1], None], 2: [[2, 3], True, [3, 2], None], 3: [[3, 4], True, [4, 3], None], 4: [[4, 5], True, [5, 4], None], 5: [[5, 6], True, [6, 5], None]}[N])
check('3', solve([[N,N+1],True,"flip",0,3]), {1: [[1, 2], False, [1, 2], None], 2: [[2, 3], False, [2, 3], None], 3: [[3, 4], False, [3, 4], None], 4: [[4, 5], False, [4, 5], None], 5: [[5, 6], False, [5, 6], None]}[N])
check('4', solve([[N],False,"push",N+1,1]), {1: [[1], False, [1], 'full'], 2: [[2], False, [2], 'full'], 3: [[3], False, [3], 'full'], 4: [[4], False, [4], 'full'], 5: [[5], False, [5], 'full']}[N])
check('5', solve([[],True,"pop",0,3]), {1: [[], True, [], 'empty'], 2: [[], True, [], 'empty'], 3: [[], True, [], 'empty'], 4: [[], True, [], 'empty'], 5: [[], True, [], 'empty']}[N])
check('6', solve([[N,N+1],False,"pop",0,3]), {1: [[2], False, [2], 1], 2: [[3], False, [3], 2], 3: [[4], False, [4], 3], 4: [[5], False, [5], 4], 5: [[6], False, [6], 5]}[N])
check('7', solve([[N],False,"push",N+1,3]), {1: [[1, 2], False, [1, 2], None], 2: [[2, 3], False, [2, 3], None], 3: [[3, 4], False, [3, 4], None], 4: [[4, 5], False, [4, 5], None], 5: [[5, 6], False, [5, 6], None]}[N])
check('full reversed rejection', solve([[N,N+1],True,'push',N+2,2]), [[N,N+1],True,[N+1,N],'full'])
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 fixtureActualExpectedOutcome
0[[1, 2], True, [2, 1], 3][[1, 2], True, [2, 1], 3]Passed
1[[1, 2, 3], True, [2, 1, 3], None][[3, 1, 2], True, [2, 1, 3], None]Failed
2[[1, 2], True, [2, 1], None][[1, 2], True, [2, 1], None]Passed
3[[1, 2], False, [1, 2], None][[1, 2], False, [1, 2], None]Passed
4[[1], False, [1], 'full'][[1], False, [1], 'full']Passed
5[[], True, [], 'empty'][[], True, [], 'empty']Passed
6[[2], False, [2], 1][[2], False, [2], 1]Passed
7[[1, 2], False, [1, 2], None][[1, 2], False, [1, 2], None]Passed
full reversed rejection[[1, 2], True, [2, 1], 'full'][[1, 2], True, [2, 1], 'full']Passed

SHA-256 / 8938f719ba97cedc57e9f5cfead7288e89640aa544a26023615831b16490a969

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 9 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.

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Verification & scope

Offline finite deterministic model; no claim of production implementation or concurrent memory-model conformance. 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 2026-09-29T14:44:37.584004+00:00.

Case digest / c5708f12ff506af4d50b5d8a548e4a5bf0a25b316cb493988d6226ef46a157f7