FA-13334 / Numerical aggregation / Member archive

Frequency symmetric trim mean: An exhausted trim is reported as a measured zero mean. · case 04

The reduction disagrees with its explicit aggregation oracle.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

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.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression 3	`"0"`	`null`	Failed

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