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FA-46611 / Bounded deques / Open access

Deque borrow accepts a negative logical start · case 01

Deque borrow accepts a negative logical start.

Verified by executionVariant 1 · 7 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Deque borrow accepts a negative logical start.

THE FAILURE

Deque borrow accepts a negative logical start.

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

Case contract

Borrow a valid logical subrange from a bounded ring as at most two physical spans. Reject negative or out-of-live-range requests. Borrow captures the current epoch and pins storage only for nonempty ranges.

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):
    cap,head,size,start,count,epoch=x
    if count<0 or start+count>size:return [False,[],epoch,0,False]
    origin=(head+start)%cap
    first=min(count,cap-origin)
    spans=[[origin,first]] if first else []
    if count>first:spans.append([0,count-first])
    captured=epoch
    pin=count>0
    return [True,spans,captured,count,pin]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([8,6,5,1,3,N]), {1: [True, [[7, 1], [0, 2]], 1, 3, True], 2: [True, [[7, 1], [0, 2]], 2, 3, True], 3: [True, [[7, 1], [0, 2]], 3, 3, True], 4: [True, [[7, 1], [0, 2]], 4, 3, True], 5: [True, [[7, 1], [0, 2]], 5, 3, True]}[N])
check('1', solve([8,2,4,1,2,N]), {1: [True, [[3, 2]], 1, 2, True], 2: [True, [[3, 2]], 2, 2, True], 3: [True, [[3, 2]], 3, 2, True], 4: [True, [[3, 2]], 4, 2, True], 5: [True, [[3, 2]], 5, 2, True]}[N])
check('2', solve([7,5,4,0,4,N]), {1: [True, [[5, 2], [0, 2]], 1, 4, True], 2: [True, [[5, 2], [0, 2]], 2, 4, True], 3: [True, [[5, 2], [0, 2]], 3, 4, True], 4: [True, [[5, 2], [0, 2]], 4, 4, True], 5: [True, [[5, 2], [0, 2]], 5, 4, True]}[N])
check('3', solve([8,3,2,2,0,N]), {1: [True, [], 1, 0, False], 2: [True, [], 2, 0, False], 3: [True, [], 3, 0, False], 4: [True, [], 4, 0, False], 5: [True, [], 5, 0, False]}[N])
check('4', solve([8,3,2,1,2,N]), {1: [False, [], 1, 0, False], 2: [False, [], 2, 0, False], 3: [False, [], 3, 0, False], 4: [False, [], 4, 0, False], 5: [False, [], 5, 0, False]}[N])
check('5', solve([6,2,3,-1,2,N]), {1: [False, [], 1, 0, False], 2: [False, [], 2, 0, False], 3: [False, [], 3, 0, False], 4: [False, [], 4, 0, False], 5: [False, [], 5, 0, False]}[N])
check('6', solve([7,1,5,3,-1,N]), {1: [False, [], 1, 0, False], 2: [False, [], 2, 0, False], 3: [False, [], 3, 0, False], 4: [False, [], 4, 0, False], 5: [False, [], 5, 0, False]}[N])
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[True, [[7, 1], [0, 2]], 1, 3, True][True, [[7, 1], [0, 2]], 1, 3, True]Passed
1[True, [[3, 2]], 1, 2, True][True, [[3, 2]], 1, 2, True]Passed
2[True, [[5, 2], [0, 2]], 1, 4, True][True, [[5, 2], [0, 2]], 1, 4, True]Passed
3[True, [], 1, 0, False][True, [], 1, 0, False]Passed
4[False, [], 1, 0, False][False, [], 1, 0, False]Passed
5[True, [[1, 2]], 1, 2, True][False, [], 1, 0, False]Failed
6[False, [], 1, 0, False][False, [], 1, 0, False]Passed

SHA-256 / 3c507f007b3beaee01f45aa8d5041cfb73c102b945346c21688744ea14206a46

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(x):
    cap,head,size,start,count,epoch=x
    if (start<0 and count==0) or count<0 or start+count>size:return [False,[],epoch,0,False]
    origin=(head+start)%cap
    first=min(count,cap-origin)
    spans=[[origin,first]] if first else []
    if count>first:spans.append([0,count-first])
    captured=epoch
    pin=count>0
    return [True,spans,captured,count,pin]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([8,6,5,1,3,N]), {1: [True, [[7, 1], [0, 2]], 1, 3, True], 2: [True, [[7, 1], [0, 2]], 2, 3, True], 3: [True, [[7, 1], [0, 2]], 3, 3, True], 4: [True, [[7, 1], [0, 2]], 4, 3, True], 5: [True, [[7, 1], [0, 2]], 5, 3, True]}[N])
check('1', solve([8,2,4,1,2,N]), {1: [True, [[3, 2]], 1, 2, True], 2: [True, [[3, 2]], 2, 2, True], 3: [True, [[3, 2]], 3, 2, True], 4: [True, [[3, 2]], 4, 2, True], 5: [True, [[3, 2]], 5, 2, True]}[N])
check('2', solve([7,5,4,0,4,N]), {1: [True, [[5, 2], [0, 2]], 1, 4, True], 2: [True, [[5, 2], [0, 2]], 2, 4, True], 3: [True, [[5, 2], [0, 2]], 3, 4, True], 4: [True, [[5, 2], [0, 2]], 4, 4, True], 5: [True, [[5, 2], [0, 2]], 5, 4, True]}[N])
check('3', solve([8,3,2,2,0,N]), {1: [True, [], 1, 0, False], 2: [True, [], 2, 0, False], 3: [True, [], 3, 0, False], 4: [True, [], 4, 0, False], 5: [True, [], 5, 0, False]}[N])
check('4', solve([8,3,2,1,2,N]), {1: [False, [], 1, 0, False], 2: [False, [], 2, 0, False], 3: [False, [], 3, 0, False], 4: [False, [], 4, 0, False], 5: [False, [], 5, 0, False]}[N])
check('5', solve([6,2,3,-1,2,N]), {1: [False, [], 1, 0, False], 2: [False, [], 2, 0, False], 3: [False, [], 3, 0, False], 4: [False, [], 4, 0, False], 5: [False, [], 5, 0, False]}[N])
check('6', solve([7,1,5,3,-1,N]), {1: [False, [], 1, 0, False], 2: [False, [], 2, 0, False], 3: [False, [], 3, 0, False], 4: [False, [], 4, 0, False], 5: [False, [], 5, 0, False]}[N])
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[True, [[7, 1], [0, 2]], 1, 3, True][True, [[7, 1], [0, 2]], 1, 3, True]Passed
1[True, [[3, 2]], 1, 2, True][True, [[3, 2]], 1, 2, True]Passed
2[True, [[5, 2], [0, 2]], 1, 4, True][True, [[5, 2], [0, 2]], 1, 4, True]Passed
3[True, [], 1, 0, False][True, [], 1, 0, False]Passed
4[False, [], 1, 0, False][False, [], 1, 0, False]Passed
5[True, [[1, 2]], 1, 2, True][False, [], 1, 0, False]Failed
6[False, [], 1, 0, False][False, [], 1, 0, False]Passed

SHA-256 / 7debda02704bfd4a2abe2de526892086c4ea4652f599055505c72e25e0affb55

HELD IN THE MEMBER ARCHIVE

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

This mechanism has 7 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 2026-09-29T14:44:33.900444+00:00.

Case digest / 226f5756f110f2d5fba6ca72153900b87dfe62334122d4cd1fa3d590e52bf5d5