{"abstract":"The operation returns a result or retained state that violates this contract: Remove exactly the first positional element.","category":"Sequence semantics","checks":5,"contract":"Remove exactly the first positional element. Inputs are the finite Python values shown by the executable fixtures; no concurrent execution is assumed.","evaluation_group":"model-949a265e6f9eeae0","failed_approach":"Deduplicating the suffix removes legitimate repeated survivors.","family":"xr-drop-first-not-all-matching","id":"FA-4136","implementations":{"attempt":{"sha256":"f4b466ec401b54953d3a93b93e0ca937fd3edd455b195e766397f11a2380280e","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return list(dict.fromkeys(x[1:]))\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('empty collection', solve([]), [])\ncheck('singleton collection', solve(['a']), [])\ncheck('two distinct elements', solve(['a', 'b']), ['b'])\ncheck('nonadjacent duplicate and unsorted order', solve(['b', 'a', 'b', 'c']), ['a', 'b', 'c'])\ncheck('duplicate suffix is retained', solve(['c','b','b']), ['b','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":"deae9487337f095e1d0bd85a60c9ab3ed1d48b2c782fc80574f192e0adc7b94d","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 != x[0]] if x else []\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('empty collection', solve([]), [])\ncheck('singleton collection', solve(['a']), [])\ncheck('two distinct elements', solve(['a', 'b']), ['b'])\ncheck('nonadjacent duplicate and unsorted order', solve(['b', 'a', 'b', 'c']), ['a', 'b', 'c'])\ncheck('duplicate suffix is retained', solve(['c','b','b']), ['b','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":"83cae5255b9300c7debb5f0eaf6ae7143c2c89d36433f0b726f7642aa69c7907","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return x[1:]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('empty collection', solve([]), [])\ncheck('singleton collection', solve(['a']), [])\ncheck('two distinct elements', solve(['a', 'b']), ['b'])\ncheck('nonadjacent duplicate and unsorted order', solve(['b', 'a', 'b', 'c']), ['a', 'b', 'c'])\ncheck('duplicate suffix is retained', solve(['c','b','b']), ['b','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-drop-first-not-all-matching","generated_at":"2026-09-29T14:37:36.172257+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":"Remove exactly the first positional element.","root_cause":"Value-based filtering removes later elements equal to the first.","sha256":"a30bd3a8308c113d2f134c874d16a88513a53c3794315563a72d1aa6724eef91","title":"Drop first not all matching · 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":35.564,"exit_code":1,"observations":[{"actual":[],"check":"empty collection","expected":[],"passed":true},{"actual":[],"check":"singleton collection","expected":[],"passed":true},{"actual":["b"],"check":"two distinct elements","expected":["b"],"passed":true},{"actual":["a","b","c"],"check":"nonadjacent duplicate and unsorted order","expected":["a","b","c"],"passed":true},{"actual":["b"],"check":"duplicate suffix is retained","expected":["b","b"],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"empty collection\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"singleton collection\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"two distinct elements\", \"actual\": [\"b\"], \"expected\": [\"b\"], \"passed\": true}, {\"check\": \"nonadjacent duplicate and unsorted order\", \"actual\": [\"a\", \"b\", \"c\"], \"expected\": [\"a\", \"b\", \"c\"], \"passed\": true}, {\"check\": \"duplicate suffix is retained\", \"actual\": [\"b\"], \"expected\": [\"b\", \"b\"], \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":38.058,"exit_code":1,"observations":[{"actual":[],"check":"empty collection","expected":[],"passed":true},{"actual":[],"check":"singleton collection","expected":[],"passed":true},{"actual":["b"],"check":"two distinct elements","expected":["b"],"passed":true},{"actual":["a","c"],"check":"nonadjacent duplicate and unsorted order","expected":["a","b","c"],"passed":false},{"actual":["b","b"],"check":"duplicate suffix is retained","expected":["b","b"],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"empty collection\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"singleton collection\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"two distinct elements\", \"actual\": [\"b\"], \"expected\": [\"b\"], \"passed\": true}, {\"check\": \"nonadjacent duplicate and unsorted order\", \"actual\": [\"a\", \"c\"], \"expected\": [\"a\", \"b\", \"c\"], \"passed\": false}, {\"check\": \"duplicate suffix is retained\", \"actual\": [\"b\", \"b\"], \"expected\": [\"b\", \"b\"], \"passed\": true}], \"passed\": false}\n"},"fixed":{"elapsed_ms":37.605,"exit_code":0,"observations":[{"actual":[],"check":"empty collection","expected":[],"passed":true},{"actual":[],"check":"singleton collection","expected":[],"passed":true},{"actual":["b"],"check":"two distinct elements","expected":["b"],"passed":true},{"actual":["a","b","c"],"check":"nonadjacent duplicate and unsorted order","expected":["a","b","c"],"passed":true},{"actual":["b","b"],"check":"duplicate suffix is retained","expected":["b","b"],"passed":true}],"passed":true,"stderr":"","stdout":"{\"observations\": [{\"check\": \"empty collection\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"singleton collection\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"two distinct elements\", \"actual\": [\"b\"], \"expected\": [\"b\"], \"passed\": true}, {\"check\": \"nonadjacent duplicate and unsorted order\", \"actual\": [\"a\", \"b\", \"c\"], \"expected\": [\"a\", \"b\", \"c\"], \"passed\": true}, {\"check\": \"duplicate suffix is retained\", \"actual\": [\"b\", \"b\"], \"expected\": [\"b\", \"b\"], \"passed\": true}], \"passed\": true}\n"}},"verified":true,"visibility":"public"}