FA-4696 / Multiset accounting / Open access
Counter intersection minimum positive count · case 01
The operation returns a result or retained state that violates this contract: Counter intersection takes the minimum count for shared members and drops nonpositive results.
ROOT CAUSE
Unfiltered minima retain nonpositive counts and absent members as zero.
VERIFIED REPAIR
Counter intersection takes the minimum count for shared members and drops nonpositive results.
Unsuccessful approach: Set intersection loses occurrence counts by assigning one to every shared member.
Case contract
Counter intersection takes the minimum count for shared members and drops nonpositive results. 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:min(v,y.get(k,0)) for k,v in x.items()}
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('counts matter', solve({'a': 3, 'b': 1}, {'a': 2, 'c': 1}), {'a': 2})
check('nonpositive omitted', solve({'a': -1}, {'a': 2}), {})
check('empty right', solve({'a': 1}, {}), {})
check('empty both', solve({}, {}), {})
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 |
|---|---|---|---|
| counts matter | {'a': 2, 'b': 0} | {'a': 2} | Failed |
| nonpositive omitted | {'a': -1} | {} | Failed |
| empty right | {'a': 0} | {} | Failed |
| empty both | {} | {} | Passed |
SHA-256 / 5de0b855a2a8466a7540df8936d513c75f0045fd285eb436aa7ad15a6ec34030
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:1 for k in x if k in y}
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('counts matter', solve({'a': 3, 'b': 1}, {'a': 2, 'c': 1}), {'a': 2})
check('nonpositive omitted', solve({'a': -1}, {'a': 2}), {})
check('empty right', solve({'a': 1}, {}), {})
check('empty both', solve({}, {}), {})
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 |
|---|---|---|---|
| counts matter | {'a': 1} | {'a': 2} | Failed |
| nonpositive omitted | {'a': 1} | {} | Failed |
| empty right | {} | {} | Passed |
| empty both | {} | {} | Passed |
SHA-256 / eb0fdf2c59539a923056fd5d350b5ff2a48095ab1fd9d8adad2f58b3ff690db3
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 dict(Counter(x)&Counter(y))
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('counts matter', solve({'a': 3, 'b': 1}, {'a': 2, 'c': 1}), {'a': 2})
check('nonpositive omitted', solve({'a': -1}, {'a': 2}), {})
check('empty right', solve({'a': 1}, {}), {})
check('empty both', solve({}, {}), {})
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 |
|---|---|---|---|
| counts matter | {'a': 2} | {'a': 2} | Passed |
| nonpositive omitted | {} | {} | Passed |
| empty right | {} | {} | Passed |
| empty both | {} | {} | Passed |
SHA-256 / 59a326a4200fa5c45dd4868c43ac0943d540c70f9aeb72e6d0378dbd951664b0
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 2026-09-29T14:37:41.865435+00:00.
Case digest / 3df3e491c411f3ec17be8019c19062436cf9170c17a0fe035507d7248e27c46a