{"abstract":"Every year shows one pay date fewer than the payroll calendar.","category":"Payroll withholding rules","checks":7,"contract":"Input {anchor [y,m,d] (any pay date), step 7|14 days, year}. Pay dates are anchor + k*step for all integers k. Return [count of pay dates within Jan 1..Dec 31 of year inclusive, ISO date of the first one, whether the count exceeds the nominal periods (26 biweekly, 52 weekly)].","contract_signature":"x","evaluation_group":"w2-payroll-withholding-pay-date-count","failed_approach":"The attempt adds the first date only when the span is not an exact multiple, dropping a pay date on December 31.","family":"w2-payroll-withholding-pay-date-count-inclusive-end-count","id":"FA-59226","implementations":{"attempt":{"sha256":"98d4a20ba723ee7ee0bd067fb7a89394fb16798724edcdb8270ed339418c2b03","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nimport datetime\nN = 1\nobservations = []\ndef solve(x):\n    anchor = datetime.date(*x['anchor'])\n    lo = datetime.date(x['year'], 1, 1)\n    hi = datetime.date(x['year'], 12, 31)\n    off = (lo - anchor).days\n    k = -(-off // x['step'])\n    first = anchor + datetime.timedelta(days=k * x['step'])\n    count = (hi - first).days // x['step'] + (1 if (hi - first).days % x['step'] else 0)\n    periods = 26 if x['step'] == 14 else 52\n    return [count, first.isoformat(), count > periods]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nfixtures = [[('regression (boundary)', {'anchor': [2026, 1, 1], 'step': 14, 'year': 2026}, [27, '2026-01-01', True]), ('regression (boundary)', {'anchor': [2020, 12, 31], 'step': 14, 'year': 2020}, [27, '2020-01-02', True]), ('partial-repair probe', {'anchor': [2021, 6, 20], 'step': 14, 'year': 2023}, [27, '2023-01-01', True]), ('partial-repair probe', {'anchor': [2021, 1, 17], 'step': 14, 'year': 2023}, [27, '2023-01-01', True]), ('additional oracle (boundary)', {'anchor': [2024, 1, 5], 'step': 14, 'year': 2024}, [26, '2024-01-05', False]), ('additional oracle', {'anchor': [2023, 8, 10], 'step': 14, 'year': 2024}, [26, '2024-01-11', False]), ('additional oracle', {'anchor': [2024, 3, 10], 'step': 14, 'year': 2024}, [26, '2024-01-14', False])], [('regression (boundary)', {'anchor': [2020, 12, 31], 'step': 14, 'year': 2020}, [27, '2020-01-02', True]), ('regression (boundary)', {'anchor': [2024, 1, 5], 'step': 14, 'year': 2024}, [26, '2024-01-05', False]), ('partial-repair probe', {'anchor': [2021, 6, 20], 'step': 14, 'year': 2023}, [27, '2023-01-01', True]), ('partial-repair probe', {'anchor': [2021, 1, 17], 'step': 14, 'year': 2023}, [27, '2023-01-01', True]), ('additional oracle', {'anchor': [2023, 8, 10], 'step': 14, 'year': 2024}, [26, '2024-01-11', False]), ('additional oracle', {'anchor': [2024, 3, 10], 'step': 14, 'year': 2024}, [26, '2024-01-14', False]), ('additional oracle', {'anchor': [2020, 3, 23], 'step': 14, 'year': 2020}, [26, '2020-01-13', False])], [('regression', {'anchor': [2021, 6, 20], 'step': 14, 'year': 2023}, [27, '2023-01-01', True]), ('regression (boundary)', {'anchor': [2024, 1, 5], 'step': 14, 'year': 2024}, [26, '2024-01-05', False]), ('partial-repair probe', {'anchor': [2022, 8, 16], 'step': 7, 'year': 2024}, [53, '2024-01-02', True]), ('partial-repair probe', {'anchor': [2025, 3, 13], 'step': 7, 'year': 2026}, [53, '2026-01-01', True]), ('additional oracle', {'anchor': [2023, 8, 10], 'step': 14, 'year': 2024}, [26, '2024-01-11', False]), ('additional oracle', {'anchor': [2024, 3, 10], 'step': 14, 'year': 2024}, [26, '2024-01-14', False]), ('additional oracle', {'anchor': [2020, 3, 23], 'step': 14, 'year': 2020}, [26, '2020-01-13', False])], [('regression', {'anchor': [2021, 1, 17], 'step': 14, 'year': 2023}, [27, '2023-01-01', True]), ('regression', {'anchor': [2023, 8, 10], 'step': 14, 'year': 2024}, [26, '2024-01-11', False]), ('partial-repair probe', {'anchor': [2020, 3, 26], 'step': 14, 'year': 2020}, [27, '2020-01-02', True]), ('partial-repair probe', {'anchor': [2024, 10, 27], 'step': 7, 'year': 2023}, [53, '2023-01-01', True]), ('additional oracle', {'anchor': [2024, 3, 10], 'step': 14, 'year': 2024}, [26, '2024-01-14', False]), ('additional oracle', {'anchor': [2020, 3, 23], 'step': 14, 'year': 2020}, [26, '2020-01-13', False]), ('additional oracle', {'anchor': [2019, 7, 21], 'step': 7, 'year': 2020}, [52, '2020-01-05', False])], [('regression', {'anchor': [2022, 8, 16], 'step': 7, 'year': 2024}, [53, '2024-01-02', True]), ('regression', {'anchor': [2024, 3, 10], 'step': 14, 'year': 2024}, [26, '2024-01-14', False]), ('partial-repair probe', {'anchor': [2023, 3, 28], 'step': 14, 'year': 2024}, [27, '2024-01-02', True]), ('partial-repair probe', {'anchor': [2021, 5, 2], 'step': 7, 'year': 2023}, [53, '2023-01-01', True]), ('additional oracle', {'anchor': [2020, 3, 23], 'step': 14, 'year': 2020}, [26, '2020-01-13', False]), ('additional oracle', {'anchor': [2019, 7, 21], 'step': 7, 'year': 2020}, [52, '2020-01-05', False]), ('additional oracle', {'anchor': [2021, 6, 11], 'step': 7, 'year': 2023}, [52, '2023-01-06', False])]]\nfor i, (label, args, expected) in enumerate(fixtures[N-1]):\n    check(\"%s %d\" % (label, i), solve(args), expected)\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":"d7654d496487da64e39f5a4c7d00465542463214d4d6fe2920a756f214dcfa70","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nimport datetime\nN = 1\nobservations = []\ndef solve(x):\n    anchor = datetime.date(*x['anchor'])\n    lo = datetime.date(x['year'], 1, 1)\n    hi = datetime.date(x['year'], 12, 31)\n    off = (lo - anchor).days\n    k = -(-off // x['step'])\n    first = anchor + datetime.timedelta(days=k * x['step'])\n    count = (hi - first).days // x['step']\n    periods = 26 if x['step'] == 14 else 52\n    return [count, first.isoformat(), count > periods]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nfixtures = [[('regression (boundary)', {'anchor': [2026, 1, 1], 'step': 14, 'year': 2026}, [27, '2026-01-01', True]), ('regression (boundary)', {'anchor': [2020, 12, 31], 'step': 14, 'year': 2020}, [27, '2020-01-02', True]), ('partial-repair probe', {'anchor': [2021, 6, 20], 'step': 14, 'year': 2023}, [27, '2023-01-01', True]), ('partial-repair probe', {'anchor': [2021, 1, 17], 'step': 14, 'year': 2023}, [27, '2023-01-01', True]), ('additional oracle (boundary)', {'anchor': [2024, 1, 5], 'step': 14, 'year': 2024}, [26, '2024-01-05', False]), ('additional oracle', {'anchor': [2023, 8, 10], 'step': 14, 'year': 2024}, [26, '2024-01-11', False]), ('additional oracle', {'anchor': [2024, 3, 10], 'step': 14, 'year': 2024}, [26, '2024-01-14', False])], [('regression (boundary)', {'anchor': [2020, 12, 31], 'step': 14, 'year': 2020}, [27, '2020-01-02', True]), ('regression (boundary)', {'anchor': [2024, 1, 5], 'step': 14, 'year': 2024}, [26, '2024-01-05', False]), ('partial-repair probe', {'anchor': [2021, 6, 20], 'step': 14, 'year': 2023}, [27, '2023-01-01', True]), ('partial-repair probe', {'anchor': [2021, 1, 17], 'step': 14, 'year': 2023}, [27, '2023-01-01', True]), ('additional oracle', {'anchor': [2023, 8, 10], 'step': 14, 'year': 2024}, [26, '2024-01-11', False]), ('additional oracle', {'anchor': [2024, 3, 10], 'step': 14, 'year': 2024}, [26, '2024-01-14', False]), ('additional oracle', {'anchor': [2020, 3, 23], 'step': 14, 'year': 2020}, [26, '2020-01-13', False])], [('regression', {'anchor': [2021, 6, 20], 'step': 14, 'year': 2023}, [27, '2023-01-01', True]), ('regression (boundary)', {'anchor': [2024, 1, 5], 'step': 14, 'year': 2024}, [26, '2024-01-05', False]), ('partial-repair probe', {'anchor': [2022, 8, 16], 'step': 7, 'year': 2024}, [53, '2024-01-02', True]), ('partial-repair probe', {'anchor': [2025, 3, 13], 'step': 7, 'year': 2026}, [53, '2026-01-01', True]), ('additional oracle', {'anchor': [2023, 8, 10], 'step': 14, 'year': 2024}, [26, '2024-01-11', False]), ('additional oracle', {'anchor': [2024, 3, 10], 'step': 14, 'year': 2024}, [26, '2024-01-14', False]), ('additional oracle', {'anchor': [2020, 3, 23], 'step': 14, 'year': 2020}, [26, '2020-01-13', False])], [('regression', {'anchor': [2021, 1, 17], 'step': 14, 'year': 2023}, [27, '2023-01-01', True]), ('regression', {'anchor': [2023, 8, 10], 'step': 14, 'year': 2024}, [26, '2024-01-11', False]), ('partial-repair probe', {'anchor': [2020, 3, 26], 'step': 14, 'year': 2020}, [27, '2020-01-02', True]), ('partial-repair probe', {'anchor': [2024, 10, 27], 'step': 7, 'year': 2023}, [53, '2023-01-01', True]), ('additional oracle', {'anchor': [2024, 3, 10], 'step': 14, 'year': 2024}, [26, '2024-01-14', False]), ('additional oracle', {'anchor': [2020, 3, 23], 'step': 14, 'year': 2020}, [26, '2020-01-13', False]), ('additional oracle', {'anchor': [2019, 7, 21], 'step': 7, 'year': 2020}, [52, '2020-01-05', False])], [('regression', {'anchor': [2022, 8, 16], 'step': 7, 'year': 2024}, [53, '2024-01-02', True]), ('regression', {'anchor': [2024, 3, 10], 'step': 14, 'year': 2024}, [26, '2024-01-14', False]), ('partial-repair probe', {'anchor': [2023, 3, 28], 'step': 14, 'year': 2024}, [27, '2024-01-02', True]), ('partial-repair probe', {'anchor': [2021, 5, 2], 'step': 7, 'year': 2023}, [53, '2023-01-01', True]), ('additional oracle', {'anchor': [2020, 3, 23], 'step': 14, 'year': 2020}, [26, '2020-01-13', False]), ('additional oracle', {'anchor': [2019, 7, 21], 'step': 7, 'year': 2020}, [52, '2020-01-05', False]), ('additional oracle', {'anchor': [2021, 6, 11], 'step': 7, 'year': 2023}, [52, '2023-01-06', False])]]\nfor i, (label, args, expected) in enumerate(fixtures[N-1]):\n    check(\"%s %d\" % (label, i), solve(args), expected)\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":"A deterministic teaching model of a stipulated payroll rule with toy thresholds and rates. It makes no claim of conformance to any tax authority, statute or jurisdiction and is not payroll software. 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":"w2-payroll-withholding-pay-date-count-inclusive-end-count","generated_at":"2026-09-29T14:46:34.213214+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"Annualization factors change in 27-pay-period years; missing or extra pay dates distort per-period withholding.","root_cause":"The first pay date itself is not counted.","sha256":"dc4d093e1c95edb66953f8009f3a3894912c8857769977c5f94f8c5c1bbf6aef","title":"Pay dates in a calendar year: inclusive end count · 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":40.979,"exit_code":1,"observations":[{"actual":[26,"2026-01-01",false],"check":"regression (boundary) 0","expected":[27,"2026-01-01",true],"passed":false},{"actual":[26,"2020-01-02",false],"check":"regression (boundary) 1","expected":[27,"2020-01-02",true],"passed":false},{"actual":[26,"2023-01-01",false],"check":"partial-repair probe 2","expected":[27,"2023-01-01",true],"passed":false},{"actual":[26,"2023-01-01",false],"check":"partial-repair probe 3","expected":[27,"2023-01-01",true],"passed":false},{"actual":[26,"2024-01-05",false],"check":"additional oracle (boundary) 4","expected":[26,"2024-01-05",false],"passed":true},{"actual":[26,"2024-01-11",false],"check":"additional oracle 5","expected":[26,"2024-01-11",false],"passed":true},{"actual":[26,"2024-01-14",false],"check":"additional oracle 6","expected":[26,"2024-01-14",false],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"regression (boundary) 0\", \"actual\": [26, \"2026-01-01\", false], \"expected\": [27, \"2026-01-01\", true], \"passed\": false}, {\"check\": \"regression (boundary) 1\", \"actual\": [26, \"2020-01-02\", false], \"expected\": [27, \"2020-01-02\", true], \"passed\": false}, {\"check\": \"partial-repair probe 2\", \"actual\": [26, \"2023-01-01\", false], \"expected\": [27, \"2023-01-01\", true], \"passed\": false}, {\"check\": \"partial-repair probe 3\", \"actual\": [26, \"2023-01-01\", false], \"expected\": [27, \"2023-01-01\", true], \"passed\": false}, {\"check\": \"additional oracle (boundary) 4\", \"actual\": [26, \"2024-01-05\", false], \"expected\": [26, \"2024-01-05\", false], \"passed\": true}, {\"check\": \"additional oracle 5\", \"actual\": [26, \"2024-01-11\", false], \"expected\": [26, \"2024-01-11\", false], \"passed\": true}, {\"check\": \"additional oracle 6\", \"actual\": [26, \"2024-01-14\", false], \"expected\": [26, \"2024-01-14\", false], \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":44.432,"exit_code":1,"observations":[{"actual":[26,"2026-01-01",false],"check":"regression (boundary) 0","expected":[27,"2026-01-01",true],"passed":false},{"actual":[26,"2020-01-02",false],"check":"regression (boundary) 1","expected":[27,"2020-01-02",true],"passed":false},{"actual":[26,"2023-01-01",false],"check":"partial-repair probe 2","expected":[27,"2023-01-01",true],"passed":false},{"actual":[26,"2023-01-01",false],"check":"partial-repair probe 3","expected":[27,"2023-01-01",true],"passed":false},{"actual":[25,"2024-01-05",false],"check":"additional oracle (boundary) 4","expected":[26,"2024-01-05",false],"passed":false},{"actual":[25,"2024-01-11",false],"check":"additional oracle 5","expected":[26,"2024-01-11",false],"passed":false},{"actual":[25,"2024-01-14",false],"check":"additional oracle 6","expected":[26,"2024-01-14",false],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"regression (boundary) 0\", \"actual\": [26, \"2026-01-01\", false], \"expected\": [27, \"2026-01-01\", true], \"passed\": false}, {\"check\": \"regression (boundary) 1\", \"actual\": [26, \"2020-01-02\", false], \"expected\": [27, \"2020-01-02\", true], \"passed\": false}, {\"check\": \"partial-repair probe 2\", \"actual\": [26, \"2023-01-01\", false], \"expected\": [27, \"2023-01-01\", true], \"passed\": false}, {\"check\": \"partial-repair probe 3\", \"actual\": [26, \"2023-01-01\", false], \"expected\": [27, \"2023-01-01\", true], \"passed\": false}, {\"check\": \"additional oracle (boundary) 4\", \"actual\": [25, \"2024-01-05\", false], \"expected\": [26, \"2024-01-05\", false], \"passed\": false}, {\"check\": \"additional oracle 5\", \"actual\": [25, \"2024-01-11\", false], \"expected\": [26, \"2024-01-11\", false], \"passed\": false}, {\"check\": \"additional oracle 6\", \"actual\": [25, \"2024-01-14\", false], \"expected\": [26, \"2024-01-14\", false], \"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."}}