FA-4161 / Sequence semantics / Open access

Left rotation one · case 01

The operation returns a result or retained state that violates this contract: Move the first item to the end; empty input remains empty.

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

ROOT CAUSE

The boundary element moves in the wrong rotation direction.

THE FAILURE

The boundary element moves in the wrong rotation direction.

Unsuccessful approach: Dropping the first element fails to reattach it at the end.

Case contract

Move the first item to the end; empty input remains empty. 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 x[-1:]+x[:-1]
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']), ['a'])
check('two distinct elements', solve(['a', 'b']), ['b', 'a'])
check('nonadjacent duplicate and unsorted order', solve(['b', 'a', 'b', 'c']), ['a', 'b', 'c', 'b'])
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	`['a']`	`['a']`	Passed
two distinct elements	`['b', 'a']`	`['b', 'a']`	Passed
nonadjacent duplicate and unsorted order	`['c', 'b', 'a', 'b']`	`['a', 'b', 'c', 'b']`	Failed

SHA-256 / d35889c0a17a1c3911f8ee0a63c619bd2d6c32feebe16ecd86d826ee5671e7d2

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[1:]
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']), ['a'])
check('two distinct elements', solve(['a', 'b']), ['b', 'a'])
check('nonadjacent duplicate and unsorted order', solve(['b', 'a', 'b', 'c']), ['a', 'b', 'c', 'b'])
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	`[]`	`['a']`	Failed
two distinct elements	`['b']`	`['b', 'a']`	Failed
nonadjacent duplicate and unsorted order	`['a', 'b', 'c']`	`['a', 'b', 'c', 'b']`	Failed

SHA-256 / d29d6458eac793d19df0ad0ff694480056c50fabb4efebf1053ad6378c9d76fb

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 4 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

Member access is invitation-based. Sign in with your invited account to inspect the repair.

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 2026-09-29T14:37:36.426161+00:00.

Case digest / 0974dafdd16445bbb91e4ac0582a5391758770aa2396db3f952d2e8f0bd63ff5