FA-13331 / Numerical aggregation / Open access
Frequency symmetric trim mean: An exhausted trim is reported as a measured zero mean. · case 01
The reduction disagrees with its explicit aggregation oracle.
ROOT CAUSE
An exhausted trim is reported as a measured zero mean.
THE FAILURE
An exhausted trim is reported as a measured zero mean.
Unsuccessful approach: A textual fraction with zero denominator is not the no-observation sentinel.
Case contract
Expand nonnegative integer frequencies. Remove exactly k lowest and k highest observations by multiplicity. Return the exact mean as a Fraction string, or None when no observations survive.
Why this case matters
Exact bounded examples isolate a reduction defect without floating-point or external-service effects.
1 / The failure
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
from fractions import Fraction
from collections import Counter, defaultdict
import math
import itertools
N = 1
observations = []
def solve(rows, k):
xs=sorted(x for x,w in rows for _ in range(w))
if not xs or 2*k>=len(xs): return "0"
return str(Fraction(sum(xs[k:len(xs)-k]),len(xs)-2*k))
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('regression 1', solve(*([(9, 1), (1, 4), (5, 2)], 2)), '7/3')
check('regression 2', solve(*([(2, 4)], 1)), '2')
check('regression 3', solve(*([], 0)), None)
check('regression 4', solve(*([(1, 2), (4, 2)], 2)), None)
check('regression 5', solve(*([(0, 1), (10, 3), (-5, 2)], 1)), '15/4')
check('regression 6', solve(*([(3, 0), (8, 1)], 0)), '8')
check('regression 7', solve(*([(1, 1), (8, 4), (9, 1)], 1)), '8')
check("variable weighted trim",solve([(N,3),(N+6,2)],1),str(Fraction(3*N+6,3)))
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 |
|---|---|---|---|
| regression 1 | 7/3 | 7/3 | Passed |
| regression 2 | 2 | 2 | Passed |
| regression 3 | 0 | None | Failed |
| regression 4 | 0 | None | Failed |
| regression 5 | 15/4 | 15/4 | Passed |
| regression 6 | 8 | 8 | Passed |
| regression 7 | 8 | 8 | Passed |
| variable weighted trim | 3 | 3 | Passed |
SHA-256 / b0348bc0456e085a37f267e6569a6873d2000fb02047b11e1c3d2c5c844c7d16
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
from fractions import Fraction
from collections import Counter, defaultdict
import math
import itertools
N = 1
observations = []
def solve(rows, k):
xs=sorted(x for x,w in rows for _ in range(w))
if not xs or 2*k>=len(xs): return "0/0"
return str(Fraction(sum(xs[k:len(xs)-k]),len(xs)-2*k))
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('regression 1', solve(*([(9, 1), (1, 4), (5, 2)], 2)), '7/3')
check('regression 2', solve(*([(2, 4)], 1)), '2')
check('regression 3', solve(*([], 0)), None)
check('regression 4', solve(*([(1, 2), (4, 2)], 2)), None)
check('regression 5', solve(*([(0, 1), (10, 3), (-5, 2)], 1)), '15/4')
check('regression 6', solve(*([(3, 0), (8, 1)], 0)), '8')
check('regression 7', solve(*([(1, 1), (8, 4), (9, 1)], 1)), '8')
check("variable weighted trim",solve([(N,3),(N+6,2)],1),str(Fraction(3*N+6,3)))
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 |
|---|---|---|---|
| regression 1 | 7/3 | 7/3 | Passed |
| regression 2 | 2 | 2 | Passed |
| regression 3 | 0/0 | None | Failed |
| regression 4 | 0/0 | None | Failed |
| regression 5 | 15/4 | 15/4 | Passed |
| regression 6 | 8 | 8 | Passed |
| regression 7 | 8 | 8 | Passed |
| variable weighted trim | 3 | 3 | Passed |
SHA-256 / 7617ad18548325b249b110f604c790388133cebe3b3564e35af4f3865ac6a8ed
HELD IN THE MEMBER ARCHIVE
The verified repair and its recorded checks are member-only.
This mechanism has 8 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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Sign in to the archive ↗Verification & scope
Small offline integer/rational inputs only; no performance, statistical inference, or production-library conformance claim. 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 2026-09-29T14:39:06.052066+00:00.
Case digest / 1f1930188a0783f0e557ad42659be9a536ddac23086433daab6cb8eaf4b8cce7