{"abstract":"The operation returns a result or retained state that violates this contract: Return whether right is a positional prefix of left.","category":"Collection algebra","checks":5,"contract":"Return whether right is a positional prefix of left. Inputs are the finite Python values shown by the executable fixtures; no concurrent execution is assumed.","contract_signature":"x, y=None","evaluation_group":"model-2764944c31ffb95e","failed_approach":"Suffix comparison checks the opposite boundary.","family":"xr-prefix-compares-positionally","id":"FA-4296","implementations":{"attempt":{"sha256":"b1e0caa8f94a3993e28f0c90d50dfb2102e59e5f2b874da1a71fd86bd6b92712","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return x[-len(y):]==y\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('both empty', solve([], []), True)\ncheck('empty right operand', solve(['a'], []), True)\ncheck('empty left operand', solve([], ['b']), False)\ncheck('overlap and multiplicity', solve(['b', 'a', 'b'], ['b', 'c', 'c']), False)\ncheck('interior is not prefix', solve(['b','a'], ['a']), False)\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"},"broken":{"sha256":"9864af9cc70f7dc50e611fe413a8b0ecae0af0f2299b436cab769764e14e74f0","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return all(v in x for v in y)\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('both empty', solve([], []), True)\ncheck('empty right operand', solve(['a'], []), True)\ncheck('empty left operand', solve([], ['b']), False)\ncheck('overlap and multiplicity', solve(['b', 'a', 'b'], ['b', 'c', 'c']), False)\ncheck('interior is not prefix', solve(['b','a'], ['a']), False)\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"}},"limitations":" 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.","method":"Deterministic executable model with adversarial boundary fixtures.","provenance":{"created_by":"Failure Map","dependencies":"Python standard library","family":"xr-prefix-compares-positionally","generated_at":"2026-09-29T14:37:37.701956+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A controlled local-runtime regression for collection APIs, language semantics, or ownership wrappers. Fixtures include boundary and interaction cases.","root_cause":"Membership ignores the starting position and order of a prefix.","sha256":"667a2df41f2f5ecfd0d85289438a27f809ce05add6af7470ea1694e2ec3279b9","title":"Prefix compares positionally · case 01","variant":1,"variant_policy":"Five execution reruns of a fixed adversarial fixture suite; variant number does not alter semantic inputs.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":37.624,"exit_code":1,"observations":[{"actual":true,"check":"both empty","expected":true,"passed":true},{"actual":false,"check":"empty right operand","expected":true,"passed":false},{"actual":false,"check":"empty left operand","expected":false,"passed":true},{"actual":false,"check":"overlap and multiplicity","expected":false,"passed":true},{"actual":true,"check":"interior is not prefix","expected":false,"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"both empty\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"empty right operand\", \"actual\": false, \"expected\": true, \"passed\": false}, {\"check\": \"empty left operand\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"overlap and multiplicity\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"interior is not prefix\", \"actual\": true, \"expected\": false, \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":38.172,"exit_code":1,"observations":[{"actual":true,"check":"both empty","expected":true,"passed":true},{"actual":true,"check":"empty right operand","expected":true,"passed":true},{"actual":false,"check":"empty left operand","expected":false,"passed":true},{"actual":false,"check":"overlap and multiplicity","expected":false,"passed":true},{"actual":true,"check":"interior is not prefix","expected":false,"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"both empty\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"empty right operand\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"empty left operand\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"overlap and multiplicity\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"interior is not prefix\", \"actual\": true, \"expected\": false, \"passed\": false}], \"passed\": false}\n"}},"member_only":{"stages":["fixed"],"fields":["implementations.fixed","verification.fixed","harness","repair"],"note":"The verified repair, its recorded checks, the repair description, and the scoring harness are available to members."}}