FA-4681 / Multiset accounting / Open access
Counter most common stable ties · case 01
The operation returns a result or retained state that violates this contract: Return at most n [key,count] pairs by descending count, breaking ties by first insertion order.
ROOT CAUSE
Lexical keys break frequency ties instead of first insertion order.
VERIFIED REPAIR
Return at most n [key,count] pairs by descending count, breaking ties by first insertion order.
Unsuccessful approach: Truncating insertion order does not rank by frequency.
Case contract
Return at most n [key,count] pairs by descending count, breaking ties by first insertion order. 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
from collections import Counter, ChainMap, deque
import heapq
N = 1
observations = []
def solve(x, y=None):
return [[k,v] for k,v in sorted(x.items(),key=lambda p:(-p[1],p[0]))[:y]]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('tie insertion order', solve({'b': 2, 'a': 2, 'c': 3}, 3), [['c', 3], ['b', 2], ['a', 2]])
check('zero requested', solve({'a': 1}, 0), [])
check('negative count included', solve({'a': -1}, 2), [['a', -1]])
check('empty', solve({}, 2), [])
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 |
|---|---|---|---|
| tie insertion order | [['c', 3], ['a', 2], ['b', 2]] | [['c', 3], ['b', 2], ['a', 2]] | Failed |
| zero requested | [] | [] | Passed |
| negative count included | [['a', -1]] | [['a', -1]] | Passed |
| empty | [] | [] | Passed |
SHA-256 / 263620826214410dc6a7b35d8c4f52fce49b289d80025848394189a9b051dcda
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
from collections import Counter, ChainMap, deque
import heapq
N = 1
observations = []
def solve(x, y=None):
return [[k,v] for k,v in list(x.items())[:y]]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('tie insertion order', solve({'b': 2, 'a': 2, 'c': 3}, 3), [['c', 3], ['b', 2], ['a', 2]])
check('zero requested', solve({'a': 1}, 0), [])
check('negative count included', solve({'a': -1}, 2), [['a', -1]])
check('empty', solve({}, 2), [])
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 |
|---|---|---|---|
| tie insertion order | [['b', 2], ['a', 2], ['c', 3]] | [['c', 3], ['b', 2], ['a', 2]] | Failed |
| zero requested | [] | [] | Passed |
| negative count included | [['a', -1]] | [['a', -1]] | Passed |
| empty | [] | [] | Passed |
SHA-256 / a26acc36bd0193d67aa7c2c6a4f4ed2ac0bc4ee5af77f42a29cd03ccdc5cce5e
3 / The verified repair
Exit 0"""Failure Map reference implementation. Python standard library only."""
import json
from collections import Counter, ChainMap, deque
import heapq
N = 1
observations = []
def solve(x, y=None):
return [list(v) for v in Counter(x).most_common(y)]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('tie insertion order', solve({'b': 2, 'a': 2, 'c': 3}, 3), [['c', 3], ['b', 2], ['a', 2]])
check('zero requested', solve({'a': 1}, 0), [])
check('negative count included', solve({'a': -1}, 2), [['a', -1]])
check('empty', solve({}, 2), [])
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 |
|---|---|---|---|
| tie insertion order | [['c', 3], ['b', 2], ['a', 2]] | [['c', 3], ['b', 2], ['a', 2]] | Passed |
| zero requested | [] | [] | Passed |
| negative count included | [['a', -1]] | [['a', -1]] | Passed |
| empty | [] | [] | Passed |
SHA-256 / d73871dc2635bb2464bdbdee3ce577b7bf2549dbe2185ae2950d4f14c51421e1
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 2026-09-29T14:37:41.584952+00:00.
Case digest / c2f97db3396a9e0cc04613144d922d5a0b5bddcd9e20438baf3a71f46fb4ad01