FAILURE MAP
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FA-40791 / Heap invariants / Open access

Interval tail survivor is the opposite endpoint of the requested removal · case 01

The bounded interval pop end certificate reports an incorrect survivor.

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

ROOT CAUSE

Interval tail survivor is the opposite endpoint of the requested removal.

THE FAILURE

Interval tail survivor is the opposite endpoint of the requested removal.

Unsuccessful approach: The local patch uses tail[0] if len(tail)==2 else None and still violates the stated relation.

Case contract

A bounded interval-tail removal receives intervals, and side low or high. Remove the requested endpoint from the final interval (singleton removed wholly), returning extracted tail replacement, remaining interval list, new logical size, singleton status, surviving endpoint, and array-node count. This isolates tail extraction before global bubbling.

Why this case matters

This isolates an internal heap representation or priority-structure invariant using deterministic finite records.

1 / The failure

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

N = 1
observations = []
def solve(d):
    a=d['intervals']; side=d['side']; tail=a[-1] if a else []; k=0 if side=='low' else -1; v=tail[k] if tail else None; rest=tail[1:] if side=='low' else tail[:-1]; out=a[:-1]+([rest] if rest else []) if a else []
    return {'replacement': v,
    'remaining': out,
    'size': sum(map(len,out)),
    'singleton': bool(out) and len(out[-1])==1,
    'survivor': v,
    'nodes': len(out)}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[({'intervals': [], 'side': 'low'}, {'replacement': None, 'remaining': [], 'size': 0, 'singleton': False, 'survivor': None, 'nodes': 0}), ({'intervals': [[4]], 'side': 'high'}, {'replacement': 4, 'remaining': [], 'size': 0, 'singleton': False, 'survivor': None, 'nodes': 0}), ({'intervals': [[1, 9]], 'side': 'low'}, {'replacement': 1, 'remaining': [[9]], 'size': 1, 'singleton': True, 'survivor': 9, 'nodes': 1}), ({'intervals': [[1, 9], [3, 7]], 'side': 'high'}, {'replacement': 7, 'remaining': [[1, 9], [3]], 'size': 3, 'singleton': True, 'survivor': 3, 'nodes': 2}), ({'intervals': [[1, 9], [3]], 'side': 'low'}, {'replacement': 3, 'remaining': [[1, 9]], 'size': 2, 'singleton': False, 'survivor': None, 'nodes': 1}), ({'intervals': [[1, 9], [2, 8], [4, 6]], 'side': 'low'}, {'replacement': 4, 'remaining': [[1, 9], [2, 8], [6]], 'size': 5, 'singleton': True, 'survivor': 6, 'nodes': 3}), ({'intervals': [[1, 9], [2, 8], [4, 7]], 'side': 'low'}, {'replacement': 4, 'remaining': [[1, 9], [2, 8], [7]], 'size': 5, 'singleton': True, 'survivor': 7, 'nodes': 3})], [({'intervals': [], 'side': 'low'}, {'replacement': None, 'remaining': [], 'size': 0, 'singleton': False, 'survivor': None, 'nodes': 0}), ({'intervals': [[4]], 'side': 'high'}, {'replacement': 4, 'remaining': [], 'size': 0, 'singleton': False, 'survivor': None, 'nodes': 0}), ({'intervals': [[1, 9]], 'side': 'low'}, {'replacement': 1, 'remaining': [[9]], 'size': 1, 'singleton': True, 'survivor': 9, 'nodes': 1}), ({'intervals': [[1, 9], [3, 7]], 'side': 'high'}, {'replacement': 7, 'remaining': [[1, 9], [3]], 'size': 3, 'singleton': True, 'survivor': 3, 'nodes': 2}), ({'intervals': [[1, 9], [3]], 'side': 'low'}, {'replacement': 3, 'remaining': [[1, 9]], 'size': 2, 'singleton': False, 'survivor': None, 'nodes': 1}), ({'intervals': [[1, 9], [2, 8], [4, 6]], 'side': 'low'}, {'replacement': 4, 'remaining': [[1, 9], [2, 8], [6]], 'size': 5, 'singleton': True, 'survivor': 6, 'nodes': 3}), ({'intervals': [[1, 9], [2, 8], [4, 8]], 'side': 'low'}, {'replacement': 4, 'remaining': [[1, 9], [2, 8], [8]], 'size': 5, 'singleton': True, 'survivor': 8, 'nodes': 3})], [({'intervals': [], 'side': 'low'}, {'replacement': None, 'remaining': [], 'size': 0, 'singleton': False, 'survivor': None, 'nodes': 0}), ({'intervals': [[4]], 'side': 'high'}, {'replacement': 4, 'remaining': [], 'size': 0, 'singleton': False, 'survivor': None, 'nodes': 0}), ({'intervals': [[1, 9]], 'side': 'low'}, {'replacement': 1, 'remaining': [[9]], 'size': 1, 'singleton': True, 'survivor': 9, 'nodes': 1}), ({'intervals': [[1, 9], [3, 7]], 'side': 'high'}, {'replacement': 7, 'remaining': [[1, 9], [3]], 'size': 3, 'singleton': True, 'survivor': 3, 'nodes': 2}), ({'intervals': [[1, 9], [3]], 'side': 'low'}, {'replacement': 3, 'remaining': [[1, 9]], 'size': 2, 'singleton': False, 'survivor': None, 'nodes': 1}), ({'intervals': [[1, 9], [2, 8], [4, 6]], 'side': 'low'}, {'replacement': 4, 'remaining': [[1, 9], [2, 8], [6]], 'size': 5, 'singleton': True, 'survivor': 6, 'nodes': 3}), ({'intervals': [[1, 9], [2, 8], [4, 9]], 'side': 'low'}, {'replacement': 4, 'remaining': [[1, 9], [2, 8], [9]], 'size': 5, 'singleton': True, 'survivor': 9, 'nodes': 3})], [({'intervals': [], 'side': 'low'}, {'replacement': None, 'remaining': [], 'size': 0, 'singleton': False, 'survivor': None, 'nodes': 0}), ({'intervals': [[4]], 'side': 'high'}, {'replacement': 4, 'remaining': [], 'size': 0, 'singleton': False, 'survivor': None, 'nodes': 0}), ({'intervals': [[1, 9]], 'side': 'low'}, {'replacement': 1, 'remaining': [[9]], 'size': 1, 'singleton': True, 'survivor': 9, 'nodes': 1}), ({'intervals': [[1, 9], [3, 7]], 'side': 'high'}, {'replacement': 7, 'remaining': [[1, 9], [3]], 'size': 3, 'singleton': True, 'survivor': 3, 'nodes': 2}), ({'intervals': [[1, 9], [3]], 'side': 'low'}, {'replacement': 3, 'remaining': [[1, 9]], 'size': 2, 'singleton': False, 'survivor': None, 'nodes': 1}), ({'intervals': [[1, 9], [2, 8], [4, 6]], 'side': 'low'}, {'replacement': 4, 'remaining': [[1, 9], [2, 8], [6]], 'size': 5, 'singleton': True, 'survivor': 6, 'nodes': 3}), ({'intervals': [[1, 9], [2, 8], [4, 10]], 'side': 'low'}, {'replacement': 4, 'remaining': [[1, 9], [2, 8], [10]], 'size': 5, 'singleton': True, 'survivor': 10, 'nodes': 3})], [({'intervals': [], 'side': 'low'}, {'replacement': None, 'remaining': [], 'size': 0, 'singleton': False, 'survivor': None, 'nodes': 0}), ({'intervals': [[4]], 'side': 'high'}, {'replacement': 4, 'remaining': [], 'size': 0, 'singleton': False, 'survivor': None, 'nodes': 0}), ({'intervals': [[1, 9]], 'side': 'low'}, {'replacement': 1, 'remaining': [[9]], 'size': 1, 'singleton': True, 'survivor': 9, 'nodes': 1}), ({'intervals': [[1, 9], [3, 7]], 'side': 'high'}, {'replacement': 7, 'remaining': [[1, 9], [3]], 'size': 3, 'singleton': True, 'survivor': 3, 'nodes': 2}), ({'intervals': [[1, 9], [3]], 'side': 'low'}, {'replacement': 3, 'remaining': [[1, 9]], 'size': 2, 'singleton': False, 'survivor': None, 'nodes': 1}), ({'intervals': [[1, 9], [2, 8], [4, 6]], 'side': 'low'}, {'replacement': 4, 'remaining': [[1, 9], [2, 8], [6]], 'size': 5, 'singleton': True, 'survivor': 6, 'nodes': 3}), ({'intervals': [[1, 9], [2, 8], [4, 11]], 'side': 'low'}, {'replacement': 4, 'remaining': [[1, 9], [2, 8], [11]], 'size': 5, 'singleton': True, 'survivor': 11, 'nodes': 3})]][N-1]
check('regression certificate 1', solve(cases[0][0]), cases[0][1])
check('regression certificate 2', solve(cases[1][0]), cases[1][1])
check('regression certificate 3', solve(cases[2][0]), cases[2][1])
check('regression certificate 4', solve(cases[3][0]), cases[3][1])
check('regression certificate 5', solve(cases[4][0]), cases[4][1])
check('regression certificate 6', solve(cases[5][0]), cases[5][1])
check('variant-dependent certificate', solve(cases[6][0]), cases[6][1])
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
regression certificate 1{'nodes': 0, 'remaining': [], 'replacement': None, 'singleton': False, 'size': 0, 'survivor': None}{'nodes': 0, 'remaining': [], 'replacement': None, 'singleton': False, 'size': 0, 'survivor': None}Passed
regression certificate 2{'nodes': 0, 'remaining': [], 'replacement': 4, 'singleton': False, 'size': 0, 'survivor': 4}{'nodes': 0, 'remaining': [], 'replacement': 4, 'singleton': False, 'size': 0, 'survivor': None}Failed
regression certificate 3{'nodes': 1, 'remaining': [[9]], 'replacement': 1, 'singleton': True, 'size': 1, 'survivor': 1}{'nodes': 1, 'remaining': [[9]], 'replacement': 1, 'singleton': True, 'size': 1, 'survivor': 9}Failed
regression certificate 4{'nodes': 2, 'remaining': [[1, 9], [3]], 'replacement': 7, 'singleton': True, 'size': 3, 'survivor': 7}{'nodes': 2, 'remaining': [[1, 9], [3]], 'replacement': 7, 'singleton': True, 'size': 3, 'survivor': 3}Failed
regression certificate 5{'nodes': 1, 'remaining': [[1, 9]], 'replacement': 3, 'singleton': False, 'size': 2, 'survivor': 3}{'nodes': 1, 'remaining': [[1, 9]], 'replacement': 3, 'singleton': False, 'size': 2, 'survivor': None}Failed
regression certificate 6{'nodes': 3, 'remaining': [[1, 9], [2, 8], [6]], 'replacement': 4, 'singleton': True, 'size': 5, 'survivor': 4}{'nodes': 3, 'remaining': [[1, 9], [2, 8], [6]], 'replacement': 4, 'singleton': True, 'size': 5, 'survivor': 6}Failed
variant-dependent certificate{'nodes': 3, 'remaining': [[1, 9], [2, 8], [7]], 'replacement': 4, 'singleton': True, 'size': 5, 'survivor': 4}{'nodes': 3, 'remaining': [[1, 9], [2, 8], [7]], 'replacement': 4, 'singleton': True, 'size': 5, 'survivor': 7}Failed

SHA-256 / 966e64f16fe4de6a6b5238e4c5af74cc9b06764d01c2603a29f8f2c336b72165

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(d):
    a=d['intervals']; side=d['side']; tail=a[-1] if a else []; k=0 if side=='low' else -1; v=tail[k] if tail else None; rest=tail[1:] if side=='low' else tail[:-1]; out=a[:-1]+([rest] if rest else []) if a else []
    return {'replacement': v,
    'remaining': out,
    'size': sum(map(len,out)),
    'singleton': bool(out) and len(out[-1])==1,
    'survivor': tail[0] if len(tail)==2 else None,
    'nodes': len(out)}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[({'intervals': [], 'side': 'low'}, {'replacement': None, 'remaining': [], 'size': 0, 'singleton': False, 'survivor': None, 'nodes': 0}), ({'intervals': [[4]], 'side': 'high'}, {'replacement': 4, 'remaining': [], 'size': 0, 'singleton': False, 'survivor': None, 'nodes': 0}), ({'intervals': [[1, 9]], 'side': 'low'}, {'replacement': 1, 'remaining': [[9]], 'size': 1, 'singleton': True, 'survivor': 9, 'nodes': 1}), ({'intervals': [[1, 9], [3, 7]], 'side': 'high'}, {'replacement': 7, 'remaining': [[1, 9], [3]], 'size': 3, 'singleton': True, 'survivor': 3, 'nodes': 2}), ({'intervals': [[1, 9], [3]], 'side': 'low'}, {'replacement': 3, 'remaining': [[1, 9]], 'size': 2, 'singleton': False, 'survivor': None, 'nodes': 1}), ({'intervals': [[1, 9], [2, 8], [4, 6]], 'side': 'low'}, {'replacement': 4, 'remaining': [[1, 9], [2, 8], [6]], 'size': 5, 'singleton': True, 'survivor': 6, 'nodes': 3}), ({'intervals': [[1, 9], [2, 8], [4, 7]], 'side': 'low'}, {'replacement': 4, 'remaining': [[1, 9], [2, 8], [7]], 'size': 5, 'singleton': True, 'survivor': 7, 'nodes': 3})], [({'intervals': [], 'side': 'low'}, {'replacement': None, 'remaining': [], 'size': 0, 'singleton': False, 'survivor': None, 'nodes': 0}), ({'intervals': [[4]], 'side': 'high'}, {'replacement': 4, 'remaining': [], 'size': 0, 'singleton': False, 'survivor': None, 'nodes': 0}), ({'intervals': [[1, 9]], 'side': 'low'}, {'replacement': 1, 'remaining': [[9]], 'size': 1, 'singleton': True, 'survivor': 9, 'nodes': 1}), ({'intervals': [[1, 9], [3, 7]], 'side': 'high'}, {'replacement': 7, 'remaining': [[1, 9], [3]], 'size': 3, 'singleton': True, 'survivor': 3, 'nodes': 2}), ({'intervals': [[1, 9], [3]], 'side': 'low'}, {'replacement': 3, 'remaining': [[1, 9]], 'size': 2, 'singleton': False, 'survivor': None, 'nodes': 1}), ({'intervals': [[1, 9], [2, 8], [4, 6]], 'side': 'low'}, {'replacement': 4, 'remaining': [[1, 9], [2, 8], [6]], 'size': 5, 'singleton': True, 'survivor': 6, 'nodes': 3}), ({'intervals': [[1, 9], [2, 8], [4, 8]], 'side': 'low'}, {'replacement': 4, 'remaining': [[1, 9], [2, 8], [8]], 'size': 5, 'singleton': True, 'survivor': 8, 'nodes': 3})], [({'intervals': [], 'side': 'low'}, {'replacement': None, 'remaining': [], 'size': 0, 'singleton': False, 'survivor': None, 'nodes': 0}), ({'intervals': [[4]], 'side': 'high'}, {'replacement': 4, 'remaining': [], 'size': 0, 'singleton': False, 'survivor': None, 'nodes': 0}), ({'intervals': [[1, 9]], 'side': 'low'}, {'replacement': 1, 'remaining': [[9]], 'size': 1, 'singleton': True, 'survivor': 9, 'nodes': 1}), ({'intervals': [[1, 9], [3, 7]], 'side': 'high'}, {'replacement': 7, 'remaining': [[1, 9], [3]], 'size': 3, 'singleton': True, 'survivor': 3, 'nodes': 2}), ({'intervals': [[1, 9], [3]], 'side': 'low'}, {'replacement': 3, 'remaining': [[1, 9]], 'size': 2, 'singleton': False, 'survivor': None, 'nodes': 1}), ({'intervals': [[1, 9], [2, 8], [4, 6]], 'side': 'low'}, {'replacement': 4, 'remaining': [[1, 9], [2, 8], [6]], 'size': 5, 'singleton': True, 'survivor': 6, 'nodes': 3}), ({'intervals': [[1, 9], [2, 8], [4, 9]], 'side': 'low'}, {'replacement': 4, 'remaining': [[1, 9], [2, 8], [9]], 'size': 5, 'singleton': True, 'survivor': 9, 'nodes': 3})], [({'intervals': [], 'side': 'low'}, {'replacement': None, 'remaining': [], 'size': 0, 'singleton': False, 'survivor': None, 'nodes': 0}), ({'intervals': [[4]], 'side': 'high'}, {'replacement': 4, 'remaining': [], 'size': 0, 'singleton': False, 'survivor': None, 'nodes': 0}), ({'intervals': [[1, 9]], 'side': 'low'}, {'replacement': 1, 'remaining': [[9]], 'size': 1, 'singleton': True, 'survivor': 9, 'nodes': 1}), ({'intervals': [[1, 9], [3, 7]], 'side': 'high'}, {'replacement': 7, 'remaining': [[1, 9], [3]], 'size': 3, 'singleton': True, 'survivor': 3, 'nodes': 2}), ({'intervals': [[1, 9], [3]], 'side': 'low'}, {'replacement': 3, 'remaining': [[1, 9]], 'size': 2, 'singleton': False, 'survivor': None, 'nodes': 1}), ({'intervals': [[1, 9], [2, 8], [4, 6]], 'side': 'low'}, {'replacement': 4, 'remaining': [[1, 9], [2, 8], [6]], 'size': 5, 'singleton': True, 'survivor': 6, 'nodes': 3}), ({'intervals': [[1, 9], [2, 8], [4, 10]], 'side': 'low'}, {'replacement': 4, 'remaining': [[1, 9], [2, 8], [10]], 'size': 5, 'singleton': True, 'survivor': 10, 'nodes': 3})], [({'intervals': [], 'side': 'low'}, {'replacement': None, 'remaining': [], 'size': 0, 'singleton': False, 'survivor': None, 'nodes': 0}), ({'intervals': [[4]], 'side': 'high'}, {'replacement': 4, 'remaining': [], 'size': 0, 'singleton': False, 'survivor': None, 'nodes': 0}), ({'intervals': [[1, 9]], 'side': 'low'}, {'replacement': 1, 'remaining': [[9]], 'size': 1, 'singleton': True, 'survivor': 9, 'nodes': 1}), ({'intervals': [[1, 9], [3, 7]], 'side': 'high'}, {'replacement': 7, 'remaining': [[1, 9], [3]], 'size': 3, 'singleton': True, 'survivor': 3, 'nodes': 2}), ({'intervals': [[1, 9], [3]], 'side': 'low'}, {'replacement': 3, 'remaining': [[1, 9]], 'size': 2, 'singleton': False, 'survivor': None, 'nodes': 1}), ({'intervals': [[1, 9], [2, 8], [4, 6]], 'side': 'low'}, {'replacement': 4, 'remaining': [[1, 9], [2, 8], [6]], 'size': 5, 'singleton': True, 'survivor': 6, 'nodes': 3}), ({'intervals': [[1, 9], [2, 8], [4, 11]], 'side': 'low'}, {'replacement': 4, 'remaining': [[1, 9], [2, 8], [11]], 'size': 5, 'singleton': True, 'survivor': 11, 'nodes': 3})]][N-1]
check('regression certificate 1', solve(cases[0][0]), cases[0][1])
check('regression certificate 2', solve(cases[1][0]), cases[1][1])
check('regression certificate 3', solve(cases[2][0]), cases[2][1])
check('regression certificate 4', solve(cases[3][0]), cases[3][1])
check('regression certificate 5', solve(cases[4][0]), cases[4][1])
check('regression certificate 6', solve(cases[5][0]), cases[5][1])
check('variant-dependent certificate', solve(cases[6][0]), cases[6][1])
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
regression certificate 1{'nodes': 0, 'remaining': [], 'replacement': None, 'singleton': False, 'size': 0, 'survivor': None}{'nodes': 0, 'remaining': [], 'replacement': None, 'singleton': False, 'size': 0, 'survivor': None}Passed
regression certificate 2{'nodes': 0, 'remaining': [], 'replacement': 4, 'singleton': False, 'size': 0, 'survivor': None}{'nodes': 0, 'remaining': [], 'replacement': 4, 'singleton': False, 'size': 0, 'survivor': None}Passed
regression certificate 3{'nodes': 1, 'remaining': [[9]], 'replacement': 1, 'singleton': True, 'size': 1, 'survivor': 1}{'nodes': 1, 'remaining': [[9]], 'replacement': 1, 'singleton': True, 'size': 1, 'survivor': 9}Failed
regression certificate 4{'nodes': 2, 'remaining': [[1, 9], [3]], 'replacement': 7, 'singleton': True, 'size': 3, 'survivor': 3}{'nodes': 2, 'remaining': [[1, 9], [3]], 'replacement': 7, 'singleton': True, 'size': 3, 'survivor': 3}Passed
regression certificate 5{'nodes': 1, 'remaining': [[1, 9]], 'replacement': 3, 'singleton': False, 'size': 2, 'survivor': None}{'nodes': 1, 'remaining': [[1, 9]], 'replacement': 3, 'singleton': False, 'size': 2, 'survivor': None}Passed
regression certificate 6{'nodes': 3, 'remaining': [[1, 9], [2, 8], [6]], 'replacement': 4, 'singleton': True, 'size': 5, 'survivor': 4}{'nodes': 3, 'remaining': [[1, 9], [2, 8], [6]], 'replacement': 4, 'singleton': True, 'size': 5, 'survivor': 6}Failed
variant-dependent certificate{'nodes': 3, 'remaining': [[1, 9], [2, 8], [7]], 'replacement': 4, 'singleton': True, 'size': 5, 'survivor': 4}{'nodes': 3, 'remaining': [[1, 9], [2, 8], [7]], 'replacement': 4, 'singleton': True, 'size': 5, 'survivor': 7}Failed

SHA-256 / c5535ead4dc88c7d87b34480fd0266030f0e72b001e39bef701a8a409a6f053d

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

A stipulated offline diagnostic model; it does not implement a production allocator, concurrency protocol, or complete heap library. 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 2026-09-29T14:43:34.517850+00:00.

Case digest / 0a14c51245cbff698524a8c863cd1276697e9c3bd379313bf3c0f815d75ede3a