FA-4601 / Iterator consumption / Open access

Combinations respect positional order · case 01

The operation returns a result or retained state that violates this contract: Return length-r combinations of input positions, preserving input order within tuples and retaining duplicate-valued tuples.

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

ROOT CAUSE

Permutations emit orderings that violate source-position order.

VERIFIED REPAIR

Return length-r combinations of input positions, preserving input order within tuples and retaining duplicate-valued tuples.

Unsuccessful approach: Deduplicating the source loses equal-valued combinations from distinct positions.

Case contract

Return length-r combinations of input positions, preserving input order within tuples and retaining duplicate-valued tuples. 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
import itertools as it
from collections import deque
N = 1
observations = []
def solve(x, y=None):
    return [list(v) for v in it.permutations(x,y)]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('position duplicates', solve(['a', 'a', 'b'], 2), [['a', 'a'], ['a', 'b'], ['a', 'b']])
check('input order', solve(['b', 'a'], 2), [['b', 'a']])
check('zero choice', solve([], 0), [[]])
check('too many', solve(['a'], 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
position duplicates	`[['a', 'a'], ['a', 'b'], ['a', 'a'], ['a', 'b'], ['b', 'a'], ['b', 'a']]`	`[['a', 'a'], ['a', 'b'], ['a', 'b']]`	Failed
input order	`[['b', 'a'], ['a', 'b']]`	`[['b', 'a']]`	Failed
zero choice	`[[]]`	`[[]]`	Passed
too many	`[]`	`[]`	Passed

SHA-256 / f171700d4b74b1382b8ff0215330532077c1b906bf17fbfcb5073cca01b2e1e3

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import itertools as it
from collections import deque
N = 1
observations = []
def solve(x, y=None):
    return [list(v) for v in it.combinations(dict.fromkeys(x),y)]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('position duplicates', solve(['a', 'a', 'b'], 2), [['a', 'a'], ['a', 'b'], ['a', 'b']])
check('input order', solve(['b', 'a'], 2), [['b', 'a']])
check('zero choice', solve([], 0), [[]])
check('too many', solve(['a'], 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
position duplicates	`[['a', 'b']]`	`[['a', 'a'], ['a', 'b'], ['a', 'b']]`	Failed
input order	`[['b', 'a']]`	`[['b', 'a']]`	Passed
zero choice	`[[]]`	`[[]]`	Passed
too many	`[]`	`[]`	Passed

SHA-256 / 1c35c7986de1e41e0dec736d06e76a82b28bbc74b55eb848f10d6ccdefebd186

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
import itertools as it
from collections import deque
N = 1
observations = []
def solve(x, y=None):
    return [list(v) for v in it.combinations(x,y)]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('position duplicates', solve(['a', 'a', 'b'], 2), [['a', 'a'], ['a', 'b'], ['a', 'b']])
check('input order', solve(['b', 'a'], 2), [['b', 'a']])
check('zero choice', solve([], 0), [[]])
check('too many', solve(['a'], 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
position duplicates	`[['a', 'a'], ['a', 'b'], ['a', 'b']]`	`[['a', 'a'], ['a', 'b'], ['a', 'b']]`	Passed
input order	`[['b', 'a']]`	`[['b', 'a']]`	Passed
zero choice	`[[]]`	`[[]]`	Passed
too many	`[]`	`[]`	Passed

SHA-256 / dcc4cd538beb9ef8d93eaef0cb6f8dca714a41cb9acb9c54b870d33a961f741f

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 2026-09-29T14:37:40.847211+00:00.

Case digest / 4e923ac9126b216273786f2486336df55ca33d522e3c70bd34288783095c3af7