FA-4201 / Sequence semantics / Open access
Stable value ranking · case 01
The operation returns a result or retained state that violates this contract: Sort values lexically and retain original positions, preserving original order among equal values.
ROOT CAUSE
Positions are assigned after sorting, losing original positions.
VERIFIED REPAIR
Sort values lexically and retain original positions, preserving original order among equal values.
Unsuccessful approach: Looking up each sorted value recovers only the first equal original position.
Case contract
Sort values lexically and retain original positions, preserving original order among equal values. 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 [[i,v] for i,v in enumerate(sorted(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']), [[0, 'a']])
check('two distinct elements', solve(['a', 'b']), [[0, 'a'], [1, 'b']])
check('nonadjacent duplicate and unsorted order', solve(['b', 'a', 'b', 'c']), [[1, 'a'], [0, 'b'], [2, 'b'], [3, 'c']])
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 | [[0, 'a']] | [[0, 'a']] | Passed |
| two distinct elements | [[0, 'a'], [1, 'b']] | [[0, 'a'], [1, 'b']] | Passed |
| nonadjacent duplicate and unsorted order | [[0, 'a'], [1, 'b'], [2, 'b'], [3, 'c']] | [[1, 'a'], [0, 'b'], [2, 'b'], [3, 'c']] | Failed |
SHA-256 / 5d344e10c69a1a90c775a50dff57dba84a8844e59dc436858d29fcdcac3fb670
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.index(v),v] for v in sorted(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']), [[0, 'a']])
check('two distinct elements', solve(['a', 'b']), [[0, 'a'], [1, 'b']])
check('nonadjacent duplicate and unsorted order', solve(['b', 'a', 'b', 'c']), [[1, 'a'], [0, 'b'], [2, 'b'], [3, 'c']])
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 | [[0, 'a']] | [[0, 'a']] | Passed |
| two distinct elements | [[0, 'a'], [1, 'b']] | [[0, 'a'], [1, 'b']] | Passed |
| nonadjacent duplicate and unsorted order | [[1, 'a'], [0, 'b'], [0, 'b'], [3, 'c']] | [[1, 'a'], [0, 'b'], [2, 'b'], [3, 'c']] | Failed |
SHA-256 / 72d1db1fd0ef00f93e542f62065e857c31116fbd9aed44c2e6602a3ec990206c
3 / The verified repair
Exit 0"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(x, y=None):
return [[i,x[i]] for i in sorted(range(len(x)), key=lambda i:x[i])]
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']), [[0, 'a']])
check('two distinct elements', solve(['a', 'b']), [[0, 'a'], [1, 'b']])
check('nonadjacent duplicate and unsorted order', solve(['b', 'a', 'b', 'c']), [[1, 'a'], [0, 'b'], [2, 'b'], [3, 'c']])
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 | [[0, 'a']] | [[0, 'a']] | Passed |
| two distinct elements | [[0, 'a'], [1, 'b']] | [[0, 'a'], [1, 'b']] | Passed |
| nonadjacent duplicate and unsorted order | [[1, 'a'], [0, 'b'], [2, 'b'], [3, 'c']] | [[1, 'a'], [0, 'b'], [2, 'b'], [3, 'c']] | Passed |
SHA-256 / c095377a823a8db84d576ebdeb1f1ae5889e1e27ed81334d25a665d11ab94898
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 2026-09-29T14:37:36.839418+00:00.
Case digest / 7e0dc57fcf7eb3699a8e6c3bc5d7e0fc8de874fe31182629f336edf9c71113df