{"abstract":"The operation returns a result or retained state that violates this contract: Return unique left values also present in right, preserving left first-appearance order.","category":"Collection algebra","checks":5,"contract":"Return unique left values also present in right, preserving left first-appearance order. Inputs are the finite Python values shown by the executable fixtures; no concurrent execution is assumed.","contract_signature":"x, y=None","evaluation_group":"model-104556b41fc51edc","failed_approach":"Taking right encounter order changes the required left-side ordering.","family":"xr-stable-set-intersection","id":"FA-4241","implementations":{"attempt":{"sha256":"d036586e7dc3431b7364a4b02c84ece38b492bed2fa57265ab650bcb8124d6a2","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return [v for v in dict.fromkeys(y) if v in x]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('both empty', solve([], []), [])\ncheck('empty right operand', solve(['a'], []), [])\ncheck('empty left operand', solve([], ['b']), [])\ncheck('overlap and multiplicity', solve(['b', 'a', 'b'], ['b', 'c', 'c']), ['b'])\ncheck('operand ordering differs', solve(['b','a'], ['a','b']), ['b','a'])\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":"f6928380137c646d15ec0ff62ff6fe5bcb3ea8df39d2cf14efd15217de9b9fbe","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return [v for v in x if v in y]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('both empty', solve([], []), [])\ncheck('empty right operand', solve(['a'], []), [])\ncheck('empty left operand', solve([], ['b']), [])\ncheck('overlap and multiplicity', solve(['b', 'a', 'b'], ['b', 'c', 'c']), ['b'])\ncheck('operand ordering differs', solve(['b','a'], ['a','b']), ['b','a'])\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-stable-set-intersection","generated_at":"2026-09-29T14:37:37.141408+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":"The output preserves duplicate left occurrences despite set semantics.","sha256":"df0bbd7f59519b75cc8836908baeea9678f1d98faa11e4a0543bf7aa9f1f6132","title":"Stable set intersection · 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":35.948,"exit_code":1,"observations":[{"actual":[],"check":"both empty","expected":[],"passed":true},{"actual":[],"check":"empty right operand","expected":[],"passed":true},{"actual":[],"check":"empty left operand","expected":[],"passed":true},{"actual":["b"],"check":"overlap and multiplicity","expected":["b"],"passed":true},{"actual":["a","b"],"check":"operand ordering differs","expected":["b","a"],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"both empty\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty right operand\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty left operand\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"overlap and multiplicity\", \"actual\": [\"b\"], \"expected\": [\"b\"], \"passed\": true}, {\"check\": \"operand ordering differs\", \"actual\": [\"a\", \"b\"], \"expected\": [\"b\", \"a\"], \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":36.117,"exit_code":1,"observations":[{"actual":[],"check":"both empty","expected":[],"passed":true},{"actual":[],"check":"empty right operand","expected":[],"passed":true},{"actual":[],"check":"empty left operand","expected":[],"passed":true},{"actual":["b","b"],"check":"overlap and multiplicity","expected":["b"],"passed":false},{"actual":["b","a"],"check":"operand ordering differs","expected":["b","a"],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"both empty\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty right operand\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty left operand\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"overlap and multiplicity\", \"actual\": [\"b\", \"b\"], \"expected\": [\"b\"], \"passed\": false}, {\"check\": \"operand ordering differs\", \"actual\": [\"b\", \"a\"], \"expected\": [\"b\", \"a\"], \"passed\": true}], \"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."}}