{"abstract":"The operation returns a result or retained state that violates this contract: Select positions 1,3,5 and so on.","category":"Sequence semantics","checks":4,"contract":"Select positions 1,3,5 and so on. Inputs are the finite Python values shown by the executable fixtures; no concurrent execution is assumed.","evaluation_group":"model-4f87ef649c44935b","failed_approach":"A unit stride keeps even positions after the first selected element.","family":"xr-odd-position-selection","id":"FA-4156","implementations":{"attempt":{"sha256":"45dc502e505c0b6da94cd199bc917aaaf251f5d22238c481cc5162b55f9e66f2","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', '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":"dd3af15299a62244aa3506d8d0934e623d59b9670d06d6677c37147e9c85cc09","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return x[::2]\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', '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":"d548edf23d0820bf73d37f6e16a644dcfc6af33e347c3f8b13af28566048af2f","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return x[1::2]\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', '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-odd-position-selection","generated_at":"2026-09-29T14:37:36.425579+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":"Select positions 1,3,5 and so on.","root_cause":"The stride begins at the wrong parity.","sha256":"c1d12111c131df483911a85eaa1ada576792f5bbeb7a8c18d5fcb9e81a11d457","title":"Odd position selection · 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":41.621,"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","c"],"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\", \"c\"], \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":40.964,"exit_code":1,"observations":[{"actual":[],"check":"empty collection","expected":[],"passed":true},{"actual":["a"],"check":"singleton collection","expected":[],"passed":false},{"actual":["a"],"check":"two distinct elements","expected":["b"],"passed":false},{"actual":["b","b"],"check":"nonadjacent duplicate and unsorted order","expected":["a","c"],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"empty collection\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"singleton collection\", \"actual\": [\"a\"], \"expected\": [], \"passed\": false}, {\"check\": \"two distinct elements\", \"actual\": [\"a\"], \"expected\": [\"b\"], \"passed\": false}, {\"check\": \"nonadjacent duplicate and unsorted order\", \"actual\": [\"b\", \"b\"], \"expected\": [\"a\", \"c\"], \"passed\": false}], \"passed\": false}\n"},"fixed":{"elapsed_ms":128.915,"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","c"],"check":"nonadjacent duplicate and unsorted order","expected":["a","c"],"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\", \"c\"], \"expected\": [\"a\", \"c\"], \"passed\": true}], \"passed\": true}\n"}},"verified":true,"visibility":"public"}