FA-46686 / Bounded deques / Open access
Deque iterator split places midpoint relative to zero · case 01
Deque iterator split places midpoint relative to zero.
ROOT CAUSE
Deque iterator split places midpoint relative to zero.
VERIFIED REPAIR
Restore the documented midpoint origin invariant in iterator-split.
Unsuccessful approach: The partial repair still applies the incorrect transition to an admitted boundary or multi-element case.
Case contract
Split an iterator range into disjoint prefix and suffix if its length meets a positive minimum. Both halves retain the same captured deque epoch and cover every original element exactly once.
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):
a,start,stop,minimum,epoch=x
length=stop-start
if length<minimum:return [None,[start,stop,epoch],a[start:stop]]
middle=length//2
prefix=[start,middle,epoch]
suffix=[middle,stop,epoch]
visited=a[start:middle]+a[middle:stop]
return [prefix,suffix,visited]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([[N,N+1,N+2,N+3,N+4],1,5,2,7]), {1: [[1, 3, 7], [3, 5, 7], [2, 3, 4, 5]], 2: [[1, 3, 7], [3, 5, 7], [3, 4, 5, 6]], 3: [[1, 3, 7], [3, 5, 7], [4, 5, 6, 7]], 4: [[1, 3, 7], [3, 5, 7], [5, 6, 7, 8]], 5: [[1, 3, 7], [3, 5, 7], [6, 7, 8, 9]]}[N])
check('1', solve([[N,N+1,N+2],0,3,2,4]), {1: [[0, 1, 4], [1, 3, 4], [1, 2, 3]], 2: [[0, 1, 4], [1, 3, 4], [2, 3, 4]], 3: [[0, 1, 4], [1, 3, 4], [3, 4, 5]], 4: [[0, 1, 4], [1, 3, 4], [4, 5, 6]], 5: [[0, 1, 4], [1, 3, 4], [5, 6, 7]]}[N])
check('2', solve([[N],0,1,2,3]), {1: [None, [0, 1, 3], [1]], 2: [None, [0, 1, 3], [2]], 3: [None, [0, 1, 3], [3]], 4: [None, [0, 1, 3], [4]], 5: [None, [0, 1, 3], [5]]}[N])
check('3', solve([[],0,0,1,0]), {1: [None, [0, 0, 0], []], 2: [None, [0, 0, 0], []], 3: [None, [0, 0, 0], []], 4: [None, [0, 0, 0], []], 5: [None, [0, 0, 0], []]}[N])
check('4', solve([[N,N+1,N+2,N+3],2,4,2,8]), {1: [[2, 3, 8], [3, 4, 8], [3, 4]], 2: [[2, 3, 8], [3, 4, 8], [4, 5]], 3: [[2, 3, 8], [3, 4, 8], [5, 6]], 4: [[2, 3, 8], [3, 4, 8], [6, 7]], 5: [[2, 3, 8], [3, 4, 8], [7, 8]]}[N])
check('5', solve([[N,N+1,N+2,N+3,N+4],0,5,3,1]), {1: [[0, 2, 1], [2, 5, 1], [1, 2, 3, 4, 5]], 2: [[0, 2, 1], [2, 5, 1], [2, 3, 4, 5, 6]], 3: [[0, 2, 1], [2, 5, 1], [3, 4, 5, 6, 7]], 4: [[0, 2, 1], [2, 5, 1], [4, 5, 6, 7, 8]], 5: [[0, 2, 1], [2, 5, 1], [5, 6, 7, 8, 9]]}[N])
check('short shifted remainder', solve([[N,N+1,N+2],2,3,2,6]), [None,[2,3,6],[N+2]])
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 |
|---|---|---|---|
| 0 | [[1, 2, 7], [2, 5, 7], [2, 3, 4, 5]] | [[1, 3, 7], [3, 5, 7], [2, 3, 4, 5]] | Failed |
| 1 | [[0, 1, 4], [1, 3, 4], [1, 2, 3]] | [[0, 1, 4], [1, 3, 4], [1, 2, 3]] | Passed |
| 2 | [None, [0, 1, 3], [1]] | [None, [0, 1, 3], [1]] | Passed |
| 3 | [None, [0, 0, 0], []] | [None, [0, 0, 0], []] | Passed |
| 4 | [[2, 1, 8], [1, 4, 8], [2, 3, 4]] | [[2, 3, 8], [3, 4, 8], [3, 4]] | Failed |
| 5 | [[0, 2, 1], [2, 5, 1], [1, 2, 3, 4, 5]] | [[0, 2, 1], [2, 5, 1], [1, 2, 3, 4, 5]] | Passed |
| short shifted remainder | [None, [2, 3, 6], [3]] | [None, [2, 3, 6], [3]] | Passed |
SHA-256 / f5a79731a43ec0a36d99d303880150b5565ad8b1cccd9f0f2fd358b69abcb6f5
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(x):
a,start,stop,minimum,epoch=x
length=stop-start
if length<minimum:return [None,[start,stop,epoch],a[start:stop]]
middle=start+length//2 if start==0 else length//2
prefix=[start,middle,epoch]
suffix=[middle,stop,epoch]
visited=a[start:middle]+a[middle:stop]
return [prefix,suffix,visited]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([[N,N+1,N+2,N+3,N+4],1,5,2,7]), {1: [[1, 3, 7], [3, 5, 7], [2, 3, 4, 5]], 2: [[1, 3, 7], [3, 5, 7], [3, 4, 5, 6]], 3: [[1, 3, 7], [3, 5, 7], [4, 5, 6, 7]], 4: [[1, 3, 7], [3, 5, 7], [5, 6, 7, 8]], 5: [[1, 3, 7], [3, 5, 7], [6, 7, 8, 9]]}[N])
check('1', solve([[N,N+1,N+2],0,3,2,4]), {1: [[0, 1, 4], [1, 3, 4], [1, 2, 3]], 2: [[0, 1, 4], [1, 3, 4], [2, 3, 4]], 3: [[0, 1, 4], [1, 3, 4], [3, 4, 5]], 4: [[0, 1, 4], [1, 3, 4], [4, 5, 6]], 5: [[0, 1, 4], [1, 3, 4], [5, 6, 7]]}[N])
check('2', solve([[N],0,1,2,3]), {1: [None, [0, 1, 3], [1]], 2: [None, [0, 1, 3], [2]], 3: [None, [0, 1, 3], [3]], 4: [None, [0, 1, 3], [4]], 5: [None, [0, 1, 3], [5]]}[N])
check('3', solve([[],0,0,1,0]), {1: [None, [0, 0, 0], []], 2: [None, [0, 0, 0], []], 3: [None, [0, 0, 0], []], 4: [None, [0, 0, 0], []], 5: [None, [0, 0, 0], []]}[N])
check('4', solve([[N,N+1,N+2,N+3],2,4,2,8]), {1: [[2, 3, 8], [3, 4, 8], [3, 4]], 2: [[2, 3, 8], [3, 4, 8], [4, 5]], 3: [[2, 3, 8], [3, 4, 8], [5, 6]], 4: [[2, 3, 8], [3, 4, 8], [6, 7]], 5: [[2, 3, 8], [3, 4, 8], [7, 8]]}[N])
check('5', solve([[N,N+1,N+2,N+3,N+4],0,5,3,1]), {1: [[0, 2, 1], [2, 5, 1], [1, 2, 3, 4, 5]], 2: [[0, 2, 1], [2, 5, 1], [2, 3, 4, 5, 6]], 3: [[0, 2, 1], [2, 5, 1], [3, 4, 5, 6, 7]], 4: [[0, 2, 1], [2, 5, 1], [4, 5, 6, 7, 8]], 5: [[0, 2, 1], [2, 5, 1], [5, 6, 7, 8, 9]]}[N])
check('short shifted remainder', solve([[N,N+1,N+2],2,3,2,6]), [None,[2,3,6],[N+2]])
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 |
|---|---|---|---|
| 0 | [[1, 2, 7], [2, 5, 7], [2, 3, 4, 5]] | [[1, 3, 7], [3, 5, 7], [2, 3, 4, 5]] | Failed |
| 1 | [[0, 1, 4], [1, 3, 4], [1, 2, 3]] | [[0, 1, 4], [1, 3, 4], [1, 2, 3]] | Passed |
| 2 | [None, [0, 1, 3], [1]] | [None, [0, 1, 3], [1]] | Passed |
| 3 | [None, [0, 0, 0], []] | [None, [0, 0, 0], []] | Passed |
| 4 | [[2, 1, 8], [1, 4, 8], [2, 3, 4]] | [[2, 3, 8], [3, 4, 8], [3, 4]] | Failed |
| 5 | [[0, 2, 1], [2, 5, 1], [1, 2, 3, 4, 5]] | [[0, 2, 1], [2, 5, 1], [1, 2, 3, 4, 5]] | Passed |
| short shifted remainder | [None, [2, 3, 6], [3]] | [None, [2, 3, 6], [3]] | Passed |
SHA-256 / 188e41490ca5b7248842793802897efa3df9db6b63b9137e4bcd7c7999a61662
3 / The verified repair
Exit 0"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(x):
a,start,stop,minimum,epoch=x
length=stop-start
if length<minimum:return [None,[start,stop,epoch],a[start:stop]]
middle=start+length//2
prefix=[start,middle,epoch]
suffix=[middle,stop,epoch]
visited=a[start:middle]+a[middle:stop]
return [prefix,suffix,visited]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([[N,N+1,N+2,N+3,N+4],1,5,2,7]), {1: [[1, 3, 7], [3, 5, 7], [2, 3, 4, 5]], 2: [[1, 3, 7], [3, 5, 7], [3, 4, 5, 6]], 3: [[1, 3, 7], [3, 5, 7], [4, 5, 6, 7]], 4: [[1, 3, 7], [3, 5, 7], [5, 6, 7, 8]], 5: [[1, 3, 7], [3, 5, 7], [6, 7, 8, 9]]}[N])
check('1', solve([[N,N+1,N+2],0,3,2,4]), {1: [[0, 1, 4], [1, 3, 4], [1, 2, 3]], 2: [[0, 1, 4], [1, 3, 4], [2, 3, 4]], 3: [[0, 1, 4], [1, 3, 4], [3, 4, 5]], 4: [[0, 1, 4], [1, 3, 4], [4, 5, 6]], 5: [[0, 1, 4], [1, 3, 4], [5, 6, 7]]}[N])
check('2', solve([[N],0,1,2,3]), {1: [None, [0, 1, 3], [1]], 2: [None, [0, 1, 3], [2]], 3: [None, [0, 1, 3], [3]], 4: [None, [0, 1, 3], [4]], 5: [None, [0, 1, 3], [5]]}[N])
check('3', solve([[],0,0,1,0]), {1: [None, [0, 0, 0], []], 2: [None, [0, 0, 0], []], 3: [None, [0, 0, 0], []], 4: [None, [0, 0, 0], []], 5: [None, [0, 0, 0], []]}[N])
check('4', solve([[N,N+1,N+2,N+3],2,4,2,8]), {1: [[2, 3, 8], [3, 4, 8], [3, 4]], 2: [[2, 3, 8], [3, 4, 8], [4, 5]], 3: [[2, 3, 8], [3, 4, 8], [5, 6]], 4: [[2, 3, 8], [3, 4, 8], [6, 7]], 5: [[2, 3, 8], [3, 4, 8], [7, 8]]}[N])
check('5', solve([[N,N+1,N+2,N+3,N+4],0,5,3,1]), {1: [[0, 2, 1], [2, 5, 1], [1, 2, 3, 4, 5]], 2: [[0, 2, 1], [2, 5, 1], [2, 3, 4, 5, 6]], 3: [[0, 2, 1], [2, 5, 1], [3, 4, 5, 6, 7]], 4: [[0, 2, 1], [2, 5, 1], [4, 5, 6, 7, 8]], 5: [[0, 2, 1], [2, 5, 1], [5, 6, 7, 8, 9]]}[N])
check('short shifted remainder', solve([[N,N+1,N+2],2,3,2,6]), [None,[2,3,6],[N+2]])
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 |
|---|---|---|---|
| 0 | [[1, 3, 7], [3, 5, 7], [2, 3, 4, 5]] | [[1, 3, 7], [3, 5, 7], [2, 3, 4, 5]] | Passed |
| 1 | [[0, 1, 4], [1, 3, 4], [1, 2, 3]] | [[0, 1, 4], [1, 3, 4], [1, 2, 3]] | Passed |
| 2 | [None, [0, 1, 3], [1]] | [None, [0, 1, 3], [1]] | Passed |
| 3 | [None, [0, 0, 0], []] | [None, [0, 0, 0], []] | Passed |
| 4 | [[2, 3, 8], [3, 4, 8], [3, 4]] | [[2, 3, 8], [3, 4, 8], [3, 4]] | Passed |
| 5 | [[0, 2, 1], [2, 5, 1], [1, 2, 3, 4, 5]] | [[0, 2, 1], [2, 5, 1], [1, 2, 3, 4, 5]] | Passed |
| short shifted remainder | [None, [2, 3, 6], [3]] | [None, [2, 3, 6], [3]] | Passed |
SHA-256 / 1ff744595f836e92e11e14398ad47914cf4c476200fa690b5f8c5e9243509200
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 2026-09-29T14:44:34.545166+00:00.
Case digest / 458ed6bdf8714c69e5cb3e2644eaf05f63cf56139593c0643b5a60c63d6bed0f