FA-4221 / Sequence semantics / Open access

Occurrence count per position · case 01

The operation returns a result or retained state that violates this contract: Return the full-list occurrence count corresponding to each original element.

Verified by executionVariant 1 · 4 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Prefix counts omit equal occurrences later in the sequence.

THE FAILURE

Prefix counts omit equal occurrences later in the sequence.

Unsuccessful approach: Deduplicating the output domain loses its position-to-count correspondence.

Case contract

Return the full-list occurrence count corresponding to each original element. Inputs are the finite Python values shown by the executable fixtures; no concurrent execution is assumed.

Why this case matters

A controlled local-runtime regression for collection APIs, language semantics, or ownership wrappers. Fixtures include boundary and interaction cases.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(x, y=None):
    return [x[:i+1].count(v) for i,v in enumerate(x)]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('empty collection', solve([]), [])
check('singleton collection', solve(['a']), [1])
check('two distinct elements', solve(['a', 'b']), [1, 1])
check('nonadjacent duplicate and unsorted order', solve(['b', 'a', 'b', 'c']), [2, 1, 2, 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 fixture	Actual	Expected	Outcome
empty collection	`[]`	`[]`	Passed
singleton collection	`[1]`	`[1]`	Passed
two distinct elements	`[1, 1]`	`[1, 1]`	Passed
nonadjacent duplicate and unsorted order	`[1, 1, 2, 1]`	`[2, 1, 2, 1]`	Failed

SHA-256 / a669845937aebcbc68e210e9e892af8a0013d690fe9938fc0a068ec130fb04cd

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(x, y=None):
    return [x.count(v) for v in dict.fromkeys(x)]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('empty collection', solve([]), [])
check('singleton collection', solve(['a']), [1])
check('two distinct elements', solve(['a', 'b']), [1, 1])
check('nonadjacent duplicate and unsorted order', solve(['b', 'a', 'b', 'c']), [2, 1, 2, 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 fixture	Actual	Expected	Outcome
empty collection	`[]`	`[]`	Passed
singleton collection	`[1]`	`[1]`	Passed
two distinct elements	`[1, 1]`	`[1, 1]`	Passed
nonadjacent duplicate and unsorted order	`[2, 1, 1]`	`[2, 1, 2, 1]`	Failed

SHA-256 / a11d9eb48ff2e5bfa2c7ca78420d1d4b7cbb99792438a84613bbb9bd12b98959

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 4 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.

Verification & scope

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 2026-09-29T14:37:37.061706+00:00.

Case digest / fada5e7c3b0ca5f29dccc824de0c4dc8153208e217d7a6fcf52be97d54360a92