FAILURE MAP
← Case archive

FA-13271 / Numerical aggregation / Open access

Frequency lower tail sum: The tail budget decreases by one row rather than selected multiplicity. · case 01

The reduction disagrees with its explicit aggregation oracle.

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

ROOT CAUSE

The tail budget decreases by one row rather than selected multiplicity.

THE FAILURE

The tail budget decreases by one row rather than selected multiplicity.

Unsuccessful approach: Subtracting an extra row count skips the next required observation.

Case contract

Rows [integer value, nonnegative frequency] expand to a multiset. Sum its smallest min(k,total frequency) observations for nonnegative integer k; zero/empty tail sums to zero.

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):
    remaining=k
    out=0
    for x,w in sorted(rows):
        take=min(remaining,w)
        out+=x*take
        remaining=max(0,remaining-1)
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('regression 1', solve(*([(2, 1), (2, 1), (9, 3)], 3)), 13)
check('regression 2', solve(*([(8, 2), (1, 3), (4, 2)], 4)), 7)
check('regression 3', solve(*([(2, 3)], 0)), 0)
check('regression 4', solve(*([], 3)), 0)
check('regression 5', solve(*([(9, 0), (2, 1)], 8)), 2)
check('regression 6', solve(*([(-5, 2), (3, 4)], 3)), -7)
check('regression 7', solve(*([(2, 1), (2, 2), (9, 1)], 2)), 4)
check('regression 8', solve(*([(1, 8), (7, 2)], 9)), 15)
check("variable tail mass",solve([(N,3),(N+5,2)],4),4*N+5)
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 11313Passed
regression 2277Failed
regression 300Passed
regression 400Passed
regression 522Passed
regression 6-4-7Failed
regression 744Passed
regression 82215Failed
variable tail mass159Failed

SHA-256 / b4769e4febc6c2ee320159cfc8411f0b1537939fb9fe52131f44c0de71441925

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):
    remaining=k
    out=0
    for x,w in sorted(rows):
        take=min(remaining,w)
        out+=x*take
        remaining=max(0,remaining-w-1)
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('regression 1', solve(*([(2, 1), (2, 1), (9, 3)], 3)), 13)
check('regression 2', solve(*([(8, 2), (1, 3), (4, 2)], 4)), 7)
check('regression 3', solve(*([(2, 3)], 0)), 0)
check('regression 4', solve(*([], 3)), 0)
check('regression 5', solve(*([(9, 0), (2, 1)], 8)), 2)
check('regression 6', solve(*([(-5, 2), (3, 4)], 3)), -7)
check('regression 7', solve(*([(2, 1), (2, 2), (9, 1)], 2)), 4)
check('regression 8', solve(*([(1, 8), (7, 2)], 9)), 15)
check("variable tail mass",solve([(N,3),(N+5,2)],4),4*N+5)
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 1413Failed
regression 237Failed
regression 300Passed
regression 400Passed
regression 522Passed
regression 6-10-7Failed
regression 724Failed
regression 8815Failed
variable tail mass39Failed

SHA-256 / ca5dffb1ca1396c365968f1f9a85e56a8b716935fccb7712ddda62acc3891104

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.

Member access is invitation-based. Sign in with your invited account to inspect the repair.

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 2026-09-29T14:39:05.472954+00:00.

Case digest / 5b7c4d39904ea8e60099ed8e6065c78517ad07ef6265e2c796f0e694bbc3130c