{"abstract":"The operation returns a result or retained state that violates this contract: Return each repeated occurrence after its first appearance, in occurrence order.","category":"Sequence semantics","checks":5,"contract":"Return each repeated occurrence after its first appearance, in occurrence 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-efb5a2cb3730a9ac","failed_approach":"Distinct-value deduplication loses third and later repeated occurrences.","family":"xr-duplicate-occurrences-exclude-first","id":"FA-4101","implementations":{"attempt":{"sha256":"6472bcf3ff06bd8beea271c274da9ec4b252837217ba8bba2e766eeb29a35457","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(v for v in x if x.count(v)>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']), [])\ncheck('nonadjacent duplicate and unsorted order', solve(['b', 'a', 'b', 'c']), ['b'])\ncheck('third occurrence remains', solve(['a','a','a']), ['a','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":"ea2d5bc26feea7384575c319452b519b0e19548c92961d8a2e528854475b1dfe","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 x.count(v)>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']), [])\ncheck('nonadjacent duplicate and unsorted order', solve(['b', 'a', 'b', 'c']), ['b'])\ncheck('third occurrence remains', solve(['a','a','a']), ['a','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-duplicate-occurrences-exclude-first","generated_at":"2026-09-29T14:37:35.600575+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":"Selecting all members with repeated values incorrectly includes their first occurrence.","sha256":"e17aa96360404ad041a199be676f71b2be01d6361287f830fb373e9dea058087","title":"Duplicate occurrences exclude first · 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":42.635,"exit_code":1,"observations":[{"actual":[],"check":"empty collection","expected":[],"passed":true},{"actual":[],"check":"singleton collection","expected":[],"passed":true},{"actual":[],"check":"two distinct elements","expected":[],"passed":true},{"actual":["b"],"check":"nonadjacent duplicate and unsorted order","expected":["b"],"passed":true},{"actual":["a"],"check":"third occurrence remains","expected":["a","a"],"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\": [], \"expected\": [], \"passed\": true}, {\"check\": \"nonadjacent duplicate and unsorted order\", \"actual\": [\"b\"], \"expected\": [\"b\"], \"passed\": true}, {\"check\": \"third occurrence remains\", \"actual\": [\"a\"], \"expected\": [\"a\", \"a\"], \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":35.11,"exit_code":1,"observations":[{"actual":[],"check":"empty collection","expected":[],"passed":true},{"actual":[],"check":"singleton collection","expected":[],"passed":true},{"actual":[],"check":"two distinct elements","expected":[],"passed":true},{"actual":["b","b"],"check":"nonadjacent duplicate and unsorted order","expected":["b"],"passed":false},{"actual":["a","a","a"],"check":"third occurrence remains","expected":["a","a"],"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\": [], \"expected\": [], \"passed\": true}, {\"check\": \"nonadjacent duplicate and unsorted order\", \"actual\": [\"b\", \"b\"], \"expected\": [\"b\"], \"passed\": false}, {\"check\": \"third occurrence remains\", \"actual\": [\"a\", \"a\", \"a\"], \"expected\": [\"a\", \"a\"], \"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."}}