{"abstract":"The operation returns a result or retained state that violates this contract: Return the first element, or None only when the list is empty.","category":"Sequence semantics","checks":4,"contract":"Return the first element, or None only when the list is empty. Inputs are the finite Python values shown by the executable fixtures; no concurrent execution is assumed.","evaluation_group":"model-a803fe4964e2fbeb","failed_approach":"The lexical minimum need not be the first inserted element.","family":"xr-first-element-default","id":"FA-4116","implementations":{"attempt":{"sha256":"8150796b866d7d5eb8a3eb3422b3be4290ce46b1de7d587b1676591036c6d96a","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return min(x) if x else None\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('empty collection', solve([]), None)\ncheck('singleton collection', solve(['a']), 'a')\ncheck('two distinct elements', solve(['a', 'b']), 'a')\ncheck('nonadjacent duplicate and unsorted order', solve(['b', 'a', 'b', 'c']), 'b')\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":"ae8228b45334b7d3bae4838c1dfeeecdff650b9a72a5194a40e65d46bbec5350","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return x[-1] if x else None\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('empty collection', solve([]), None)\ncheck('singleton collection', solve(['a']), 'a')\ncheck('two distinct elements', solve(['a', 'b']), 'a')\ncheck('nonadjacent duplicate and unsorted order', solve(['b', 'a', 'b', 'c']), 'b')\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"},"fixed":{"sha256":"e3e44fdb75b92078008d04e9f5f914f9763cadc25408bc9f88c9417becf7574e","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return x[0] if x else None\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('empty collection', solve([]), None)\ncheck('singleton collection', solve(['a']), 'a')\ncheck('two distinct elements', solve(['a', 'b']), 'a')\ncheck('nonadjacent duplicate and unsorted order', solve(['b', 'a', 'b', 'c']), 'b')\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-first-element-default","generated_at":"2026-09-29T14:37:35.745469+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.","repair":"Return the first element, or None only when the list is empty.","root_cause":"The last positional element is selected instead of the first.","sha256":"03391c665ebd3e36a96e0d99e1d807ab424952c190630961054531473ffab31b","title":"First element default · case 01","variant":1,"variant_policy":"Five execution reruns of a fixed adversarial fixture suite; variant number does not alter semantic inputs.","verification":{"attempt":{"elapsed_ms":123.939,"exit_code":1,"observations":[{"actual":null,"check":"empty collection","expected":null,"passed":true},{"actual":"a","check":"singleton collection","expected":"a","passed":true},{"actual":"a","check":"two distinct elements","expected":"a","passed":true},{"actual":"a","check":"nonadjacent duplicate and unsorted order","expected":"b","passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"empty collection\", \"actual\": null, \"expected\": null, \"passed\": true}, {\"check\": \"singleton collection\", \"actual\": \"a\", \"expected\": \"a\", \"passed\": true}, {\"check\": \"two distinct elements\", \"actual\": \"a\", \"expected\": \"a\", \"passed\": true}, {\"check\": \"nonadjacent duplicate and unsorted order\", \"actual\": \"a\", \"expected\": \"b\", \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":41.488,"exit_code":1,"observations":[{"actual":null,"check":"empty collection","expected":null,"passed":true},{"actual":"a","check":"singleton collection","expected":"a","passed":true},{"actual":"b","check":"two distinct elements","expected":"a","passed":false},{"actual":"c","check":"nonadjacent duplicate and unsorted order","expected":"b","passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"empty collection\", \"actual\": null, \"expected\": null, \"passed\": true}, {\"check\": \"singleton collection\", \"actual\": \"a\", \"expected\": \"a\", \"passed\": true}, {\"check\": \"two distinct elements\", \"actual\": \"b\", \"expected\": \"a\", \"passed\": false}, {\"check\": \"nonadjacent duplicate and unsorted order\", \"actual\": \"c\", \"expected\": \"b\", \"passed\": false}], \"passed\": false}\n"},"fixed":{"elapsed_ms":38.731,"exit_code":0,"observations":[{"actual":null,"check":"empty collection","expected":null,"passed":true},{"actual":"a","check":"singleton collection","expected":"a","passed":true},{"actual":"a","check":"two distinct elements","expected":"a","passed":true},{"actual":"b","check":"nonadjacent duplicate and unsorted order","expected":"b","passed":true}],"passed":true,"stderr":"","stdout":"{\"observations\": [{\"check\": \"empty collection\", \"actual\": null, \"expected\": null, \"passed\": true}, {\"check\": \"singleton collection\", \"actual\": \"a\", \"expected\": \"a\", \"passed\": true}, {\"check\": \"two distinct elements\", \"actual\": \"a\", \"expected\": \"a\", \"passed\": true}, {\"check\": \"nonadjacent duplicate and unsorted order\", \"actual\": \"b\", \"expected\": \"b\", \"passed\": true}], \"passed\": true}\n"}},"verified":true,"visibility":"public"}