{"abstract":"The operation returns a result or retained state that violates this contract: Concatenate left then right, retaining every occurrence.","category":"Collection algebra","checks":4,"contract":"Concatenate left then right, retaining every occurrence. Inputs are the finite Python values shown by the executable fixtures; no concurrent execution is assumed.","evaluation_group":"model-9e0318083d2c4c1a","failed_approach":"Deduplication discards intentional repeated values.","family":"xr-concatenation-order-and-duplicates","id":"FA-4231","implementations":{"attempt":{"sha256":"9213159ce2cd08626e7f58c4b3012e8fbdb177de455611caa8786f796fbc528a","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+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'], []), ['a'])\ncheck('empty left operand', solve([], ['b']), ['b'])\ncheck('overlap and multiplicity', solve(['b', 'a', 'b'], ['b', 'c', 'c']), ['b', 'a', 'b', 'b', 'c', 'c'])\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":"0b3f2238274b87e4ffb4d86ffb299e46a808a6d5465f72fc60aff4c37fcef750","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return y+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'], []), ['a'])\ncheck('empty left operand', solve([], ['b']), ['b'])\ncheck('overlap and multiplicity', solve(['b', 'a', 'b'], ['b', 'c', 'c']), ['b', 'a', 'b', 'b', 'c', 'c'])\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":"073444a9d0e93dc7438938815b3510a68de19a76e8be2291adea235861895cab","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return x+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'], []), ['a'])\ncheck('empty left operand', solve([], ['b']), ['b'])\ncheck('overlap and multiplicity', solve(['b', 'a', 'b'], ['b', 'c', 'c']), ['b', 'a', 'b', 'b', 'c', 'c'])\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-concatenation-order-and-duplicates","generated_at":"2026-09-29T14:37:37.103975+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":"Concatenate left then right, retaining every occurrence.","root_cause":"The operands are appended in reverse order.","sha256":"10955c049d2f83edb7ce1fe66c99f912a2767d4de100e43eed66b49b3e02e723","title":"Concatenation order and duplicates · 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":35.984,"exit_code":1,"observations":[{"actual":[],"check":"both empty","expected":[],"passed":true},{"actual":["a"],"check":"empty right operand","expected":["a"],"passed":true},{"actual":["b"],"check":"empty left operand","expected":["b"],"passed":true},{"actual":["b","a","c"],"check":"overlap and multiplicity","expected":["b","a","b","b","c","c"],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"both empty\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty right operand\", \"actual\": [\"a\"], \"expected\": [\"a\"], \"passed\": true}, {\"check\": \"empty left operand\", \"actual\": [\"b\"], \"expected\": [\"b\"], \"passed\": true}, {\"check\": \"overlap and multiplicity\", \"actual\": [\"b\", \"a\", \"c\"], \"expected\": [\"b\", \"a\", \"b\", \"b\", \"c\", \"c\"], \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":36.495,"exit_code":1,"observations":[{"actual":[],"check":"both empty","expected":[],"passed":true},{"actual":["a"],"check":"empty right operand","expected":["a"],"passed":true},{"actual":["b"],"check":"empty left operand","expected":["b"],"passed":true},{"actual":["b","c","c","b","a","b"],"check":"overlap and multiplicity","expected":["b","a","b","b","c","c"],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"both empty\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty right operand\", \"actual\": [\"a\"], \"expected\": [\"a\"], \"passed\": true}, {\"check\": \"empty left operand\", \"actual\": [\"b\"], \"expected\": [\"b\"], \"passed\": true}, {\"check\": \"overlap and multiplicity\", \"actual\": [\"b\", \"c\", \"c\", \"b\", \"a\", \"b\"], \"expected\": [\"b\", \"a\", \"b\", \"b\", \"c\", \"c\"], \"passed\": false}], \"passed\": false}\n"},"fixed":{"elapsed_ms":35.828,"exit_code":0,"observations":[{"actual":[],"check":"both empty","expected":[],"passed":true},{"actual":["a"],"check":"empty right operand","expected":["a"],"passed":true},{"actual":["b"],"check":"empty left operand","expected":["b"],"passed":true},{"actual":["b","a","b","b","c","c"],"check":"overlap and multiplicity","expected":["b","a","b","b","c","c"],"passed":true}],"passed":true,"stderr":"","stdout":"{\"observations\": [{\"check\": \"both empty\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty right operand\", \"actual\": [\"a\"], \"expected\": [\"a\"], \"passed\": true}, {\"check\": \"empty left operand\", \"actual\": [\"b\"], \"expected\": [\"b\"], \"passed\": true}, {\"check\": \"overlap and multiplicity\", \"actual\": [\"b\", \"a\", \"b\", \"b\", \"c\", \"c\"], \"expected\": [\"b\", \"a\", \"b\", \"b\", \"c\", \"c\"], \"passed\": true}], \"passed\": true}\n"}},"verified":true,"visibility":"public"}