{"abstract":"Divisibility by four ignores the century exception.","category":"Calendar arithmetic","checks":4,"contract":"Valid ISO Gregorian dates in years 1 through 9999; generated dates must remain in that range. Month is 1 through 12 and zero-based weekday is Monday 0 through Sunday 6 unless the output convention says otherwise. Gregorian leap century rule. Exact operational definition: calendar.isleap(year)","contract_signature":"year","evaluation_group":"model-8463831a8854f182","failed_approach":"Excluding all centuries ignores the four-hundred-year restoration.","family":"xn-gregorian-leap-century-rule","id":"FA-6476","implementations":{"attempt":{"sha256":"b5822285a54b538f7ad6a364272de8f45dcc389c2ba75b1ce4fe37dd3f5f3ee6","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nimport math\nimport calendar\nimport statistics\nimport itertools\nfrom fractions import Fraction\nfrom datetime import date, datetime, timedelta, timezone\nfrom decimal import Decimal, ROUND_HALF_UP, ROUND_DOWN, ROUND_CEILING, ROUND_FLOOR\n\nN = 1\nobservations = []\ndef solve(year):\n    return year%4==0 and year%100!=0\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('fixture 1: (2000,)', solve(*(2000,)), True)\ncheck('fixture 2: (2100,)', solve(*(2100,)), False)\ncheck('fixture 3: (2024,)', solve(*(2024,)), True)\ncheck('fixture 4: (2023,)', solve(*(2023,)), False)\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":"c99375b88ce9bb5f873bc25e4ca12d02f2069a92f13d87ef97d563415bdca766","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nimport math\nimport calendar\nimport statistics\nimport itertools\nfrom fractions import Fraction\nfrom datetime import date, datetime, timedelta, timezone\nfrom decimal import Decimal, ROUND_HALF_UP, ROUND_DOWN, ROUND_CEILING, ROUND_FLOOR\n\nN = 1\nobservations = []\ndef solve(year):\n    return year%4==0\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('fixture 1: (2000,)', solve(*(2000,)), True)\ncheck('fixture 2: (2100,)', solve(*(2100,)), False)\ncheck('fixture 3: (2024,)', solve(*(2024,)), True)\ncheck('fixture 4: (2023,)', solve(*(2023,)), False)\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":"xn-gregorian-leap-century-rule","generated_at":"2026-09-29T14:38:02.415708+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"Small exact fixtures expose this error without platform timing, external services, or probabilistic observations. Calendar conventions results depend on the stated convention.","root_cause":"Divisibility by four ignores the century exception.","sha256":"cceaf0f1aa79974f76e48c4ef0810619b10e0ac8c111de8faf50690de0cbcf93","title":"Gregorian leap century rule · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":115.497,"exit_code":1,"observations":[{"actual":false,"check":"fixture 1: (2000,)","expected":true,"passed":false},{"actual":false,"check":"fixture 2: (2100,)","expected":false,"passed":true},{"actual":true,"check":"fixture 3: (2024,)","expected":true,"passed":true},{"actual":false,"check":"fixture 4: (2023,)","expected":false,"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 1: (2000,)\", \"actual\": false, \"expected\": true, \"passed\": false}, {\"check\": \"fixture 2: (2100,)\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"fixture 3: (2024,)\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"fixture 4: (2023,)\", \"actual\": false, \"expected\": false, \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":47.211,"exit_code":1,"observations":[{"actual":true,"check":"fixture 1: (2000,)","expected":true,"passed":true},{"actual":true,"check":"fixture 2: (2100,)","expected":false,"passed":false},{"actual":true,"check":"fixture 3: (2024,)","expected":true,"passed":true},{"actual":false,"check":"fixture 4: (2023,)","expected":false,"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 1: (2000,)\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"fixture 2: (2100,)\", \"actual\": true, \"expected\": false, \"passed\": false}, {\"check\": \"fixture 3: (2024,)\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"fixture 4: (2023,)\", \"actual\": false, \"expected\": false, \"passed\": true}], \"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."}}