FA-4671 / Multiset accounting / Open access
Counter update adds not replaces · case 01
The operation returns a result or retained state that violates this contract: Counter update adds supplied counts to existing counts, retaining zero and negative entries.
ROOT CAUSE
Dictionary assignment replaces counts instead of accumulating them.
VERIFIED REPAIR
Counter update adds supplied counts to existing counts, retaining zero and negative entries.
Unsuccessful approach: Positive-bag addition drops zero and negative entries required by update semantics.
Case contract
Counter update adds supplied counts to existing counts, retaining zero and negative entries. 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):
a=Counter(x); a=dict(a); a.update(y); return a
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('existing count accumulates', solve({'a': 2}, {'a': 3}), {'a': 5})
check('zero retained', solve({'a': 2}, {'a': -2}), {'a': 0})
check('negative retained', solve({}, {'a': -1}), {'a': -1})
check('empty', 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 |
|---|---|---|---|
| existing count accumulates | {'a': 3} | {'a': 5} | Failed |
| zero retained | {'a': -2} | {'a': 0} | Failed |
| negative retained | {'a': -1} | {'a': -1} | Passed |
| empty | {} | {} | Passed |
SHA-256 / a0ad2bfcfad056a0d09faa8dd8d5622de38a481a755d63bd80bdb3d0f579409c
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 dict(Counter(x)+Counter(y))
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('existing count accumulates', solve({'a': 2}, {'a': 3}), {'a': 5})
check('zero retained', solve({'a': 2}, {'a': -2}), {'a': 0})
check('negative retained', solve({}, {'a': -1}), {'a': -1})
check('empty', 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 |
|---|---|---|---|
| existing count accumulates | {'a': 5} | {'a': 5} | Passed |
| zero retained | {} | {'a': 0} | Failed |
| negative retained | {} | {'a': -1} | Failed |
| empty | {} | {} | Passed |
SHA-256 / 7636eceb4396506465f9f03924abf28769d8afde1f27c6a69597cf4dc5a5a45b
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):
a=Counter(x); a.update(y); return dict(a)
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('existing count accumulates', solve({'a': 2}, {'a': 3}), {'a': 5})
check('zero retained', solve({'a': 2}, {'a': -2}), {'a': 0})
check('negative retained', solve({}, {'a': -1}), {'a': -1})
check('empty', 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 |
|---|---|---|---|
| existing count accumulates | {'a': 5} | {'a': 5} | Passed |
| zero retained | {'a': 0} | {'a': 0} | Passed |
| negative retained | {'a': -1} | {'a': -1} | Passed |
| empty | {} | {} | Passed |
SHA-256 / e7d0190a0d1f1bf90c34c74caa3dcb5605a8128ae05c0ad0f559312bf2ba9fce
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 2026-09-29T14:37:41.508716+00:00.
Case digest / 00e1467cf48361156a07a9a97c39e7a1b4fcc567033f0363b6b0f5e99f90c406