FA-62686 / Tax bracket computation / Open access
The local surtax is computed on state tax before credits · case 01
Filers with large nonrefundable credits pay local surtax on tax they never owed.
ROOT CAUSE
The surtax base is the gross state tax.
VERIFIED REPAIR
Base the surtax on state tax after nonrefundable credits.
Unsuccessful approach: Also deducting refundable credits from the base under-charges the surtax.
Case contract
solve(state, nonref, ref, pct): amounts in integer cents; pct a decimal percentage string. State tax after nonrefundable credits is max(0, state - nonref). The local surtax is pct% of that amount, rounded half-up to cents. Refundable credits then apply to the combined total in full (a negative total is a refund). Return [local, total].
Why this case matters
Tax computations hinge on which slice, threshold, ordering and rounding rule applies at each step; a misplaced boundary silently misstates liabilities.
1 / The failure
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
from fractions import Fraction
N = 1
observations = []
def solve(state, nonref, ref, pct):
after = max(0, state - nonref)
local = int(state * Fraction(pct) / 100 + Fraction(1, 2))
return [local, after + local - ref]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('regression surtax-base 1', (100000, 20000, 5000, '17.5'), [14000, 89000]),
('regression surtax-base 2', (1000, 3000, 500, '20'), [0, -500]),
('partial repair guard 2', (5000, 1000, 9000, '12.5'), [500, -4500]),
('control: rounding', (333, 0, 0, '1.5'), [5, 338]), ('control: half cent', (1001, 0, 0, '50'), [501, 1502]),
('control: no surtax', (4200, 100, 0, '0'), [0, 4100])],
[('regression surtax-base 1', (5000, 1000, 9000, '12.5'), [500, -4500]),
('regression surtax-base 2', (143686, 20000, 9000, '17.5'), [21645, 136331]),
('partial repair guard 2', (86323, 79662, 500, '12.5'), [833, 6994]),
('control: half cent', (1001, 0, 0, '50'), [501, 1502]), ('control: no surtax', (4200, 100, 0, '0'), [0, 4100]),
('control: typical', (100000, 20000, 5000, '17.5'), [14000, 89000]),
('control: credits exceed tax', (1000, 3000, 500, '20'), [0, -500])],
[('regression surtax-base 1', (133783, 45064, 0, '17.5'), [15526, 104245]),
('regression surtax-base 2', (27192, 1000, 0, '12.5'), [3274, 29466]),
('partial repair guard 1', (44678, 28763, 500, '50'), [7958, 23373]),
('partial repair guard 2', (176644, 20000, 500, '8'), [12532, 168676]),
('control: typical', (100000, 20000, 5000, '17.5'), [14000, 89000]),
('control: credits exceed tax', (1000, 3000, 500, '20'), [0, -500]),
('control: rounding', (333, 0, 0, '1.5'), [5, 338]),
('control: large refund', (5000, 1000, 9000, '12.5'), [500, -4500])],
[('regression surtax-base 1', (86323, 79662, 500, '12.5'), [833, 6994]),
('regression surtax-base 2', (44678, 28763, 500, '50'), [7958, 23373]),
('partial repair guard 1', (107676, 1000, 9000, '8'), [8534, 106210]),
('partial repair guard 2', (96269, 20000, 9000, '8'), [6102, 73371]),
('control: large refund', (5000, 1000, 9000, '12.5'), [500, -4500]),
('control: half cent', (1001, 0, 0, '50'), [501, 1502]), ('control: no surtax', (4200, 100, 0, '0'), [0, 4100]),
('control: typical', (100000, 20000, 5000, '17.5'), [14000, 89000])],
[('regression surtax-base 1', (176644, 20000, 500, '8'), [12532, 168676]),
('regression surtax-base 2', (107676, 1000, 9000, '8'), [8534, 106210]),
('partial repair guard 1', (171795, 55836, 500, '1.5'), [1739, 117198]),
('partial repair guard 2', (195423, 1000, 9000, '17.5'), [34024, 219447]),
('control: typical', (100000, 20000, 5000, '17.5'), [14000, 89000]),
('control: credits exceed tax', (1000, 3000, 500, '20'), [0, -500]),
('control: rounding', (333, 0, 0, '1.5'), [5, 338]),
('control: large refund', (5000, 1000, 9000, '12.5'), [500, -4500])]]
for label, args, expected in cases[N - 1]:
check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| regression surtax-base 1 | [17500, 92500] | [14000, 89000] | Failed |
| regression surtax-base 2 | [200, -300] | [0, -500] | Failed |
| partial repair guard 2 | [625, -4375] | [500, -4500] | Failed |
| control: rounding | [5, 338] | [5, 338] | Passed |
| control: half cent | [501, 1502] | [501, 1502] | Passed |
| control: no surtax | [0, 4100] | [0, 4100] | Passed |
SHA-256 / 4423fc47e87040d0f52ce7fc5e587e7ae87f188e7b3c531e362f8ca63e310305
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
from fractions import Fraction
N = 1
observations = []
def solve(state, nonref, ref, pct):
after = max(0, state - nonref)
local = int(max(0, after - ref) * Fraction(pct) / 100 + Fraction(1, 2))
return [local, after + local - ref]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('regression surtax-base 1', (100000, 20000, 5000, '17.5'), [14000, 89000]),
('regression surtax-base 2', (1000, 3000, 500, '20'), [0, -500]),
('partial repair guard 2', (5000, 1000, 9000, '12.5'), [500, -4500]),
('control: rounding', (333, 0, 0, '1.5'), [5, 338]), ('control: half cent', (1001, 0, 0, '50'), [501, 1502]),
('control: no surtax', (4200, 100, 0, '0'), [0, 4100])],
[('regression surtax-base 1', (5000, 1000, 9000, '12.5'), [500, -4500]),
('regression surtax-base 2', (143686, 20000, 9000, '17.5'), [21645, 136331]),
('partial repair guard 2', (86323, 79662, 500, '12.5'), [833, 6994]),
('control: half cent', (1001, 0, 0, '50'), [501, 1502]), ('control: no surtax', (4200, 100, 0, '0'), [0, 4100]),
('control: typical', (100000, 20000, 5000, '17.5'), [14000, 89000]),
('control: credits exceed tax', (1000, 3000, 500, '20'), [0, -500])],
[('regression surtax-base 1', (133783, 45064, 0, '17.5'), [15526, 104245]),
('regression surtax-base 2', (27192, 1000, 0, '12.5'), [3274, 29466]),
('partial repair guard 1', (44678, 28763, 500, '50'), [7958, 23373]),
('partial repair guard 2', (176644, 20000, 500, '8'), [12532, 168676]),
('control: typical', (100000, 20000, 5000, '17.5'), [14000, 89000]),
('control: credits exceed tax', (1000, 3000, 500, '20'), [0, -500]),
('control: rounding', (333, 0, 0, '1.5'), [5, 338]),
('control: large refund', (5000, 1000, 9000, '12.5'), [500, -4500])],
[('regression surtax-base 1', (86323, 79662, 500, '12.5'), [833, 6994]),
('regression surtax-base 2', (44678, 28763, 500, '50'), [7958, 23373]),
('partial repair guard 1', (107676, 1000, 9000, '8'), [8534, 106210]),
('partial repair guard 2', (96269, 20000, 9000, '8'), [6102, 73371]),
('control: large refund', (5000, 1000, 9000, '12.5'), [500, -4500]),
('control: half cent', (1001, 0, 0, '50'), [501, 1502]), ('control: no surtax', (4200, 100, 0, '0'), [0, 4100]),
('control: typical', (100000, 20000, 5000, '17.5'), [14000, 89000])],
[('regression surtax-base 1', (176644, 20000, 500, '8'), [12532, 168676]),
('regression surtax-base 2', (107676, 1000, 9000, '8'), [8534, 106210]),
('partial repair guard 1', (171795, 55836, 500, '1.5'), [1739, 117198]),
('partial repair guard 2', (195423, 1000, 9000, '17.5'), [34024, 219447]),
('control: typical', (100000, 20000, 5000, '17.5'), [14000, 89000]),
('control: credits exceed tax', (1000, 3000, 500, '20'), [0, -500]),
('control: rounding', (333, 0, 0, '1.5'), [5, 338]),
('control: large refund', (5000, 1000, 9000, '12.5'), [500, -4500])]]
for label, args, expected in cases[N - 1]:
check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| regression surtax-base 1 | [13125, 88125] | [14000, 89000] | Failed |
| regression surtax-base 2 | [0, -500] | [0, -500] | Passed |
| partial repair guard 2 | [0, -5000] | [500, -4500] | Failed |
| control: rounding | [5, 338] | [5, 338] | Passed |
| control: half cent | [501, 1502] | [501, 1502] | Passed |
| control: no surtax | [0, 4100] | [0, 4100] | Passed |
SHA-256 / af70bf138f2dfd057500e04caf3bc0ea3635d4dfe9b75174de30f86476b0e19a
3 / The verified repair
Exit 0"""Failure Map reference implementation. Python standard library only."""
import json
from fractions import Fraction
N = 1
observations = []
def solve(state, nonref, ref, pct):
after = max(0, state - nonref)
local = int(after * Fraction(pct) / 100 + Fraction(1, 2))
return [local, after + local - ref]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('regression surtax-base 1', (100000, 20000, 5000, '17.5'), [14000, 89000]),
('regression surtax-base 2', (1000, 3000, 500, '20'), [0, -500]),
('partial repair guard 2', (5000, 1000, 9000, '12.5'), [500, -4500]),
('control: rounding', (333, 0, 0, '1.5'), [5, 338]), ('control: half cent', (1001, 0, 0, '50'), [501, 1502]),
('control: no surtax', (4200, 100, 0, '0'), [0, 4100])],
[('regression surtax-base 1', (5000, 1000, 9000, '12.5'), [500, -4500]),
('regression surtax-base 2', (143686, 20000, 9000, '17.5'), [21645, 136331]),
('partial repair guard 2', (86323, 79662, 500, '12.5'), [833, 6994]),
('control: half cent', (1001, 0, 0, '50'), [501, 1502]), ('control: no surtax', (4200, 100, 0, '0'), [0, 4100]),
('control: typical', (100000, 20000, 5000, '17.5'), [14000, 89000]),
('control: credits exceed tax', (1000, 3000, 500, '20'), [0, -500])],
[('regression surtax-base 1', (133783, 45064, 0, '17.5'), [15526, 104245]),
('regression surtax-base 2', (27192, 1000, 0, '12.5'), [3274, 29466]),
('partial repair guard 1', (44678, 28763, 500, '50'), [7958, 23373]),
('partial repair guard 2', (176644, 20000, 500, '8'), [12532, 168676]),
('control: typical', (100000, 20000, 5000, '17.5'), [14000, 89000]),
('control: credits exceed tax', (1000, 3000, 500, '20'), [0, -500]),
('control: rounding', (333, 0, 0, '1.5'), [5, 338]),
('control: large refund', (5000, 1000, 9000, '12.5'), [500, -4500])],
[('regression surtax-base 1', (86323, 79662, 500, '12.5'), [833, 6994]),
('regression surtax-base 2', (44678, 28763, 500, '50'), [7958, 23373]),
('partial repair guard 1', (107676, 1000, 9000, '8'), [8534, 106210]),
('partial repair guard 2', (96269, 20000, 9000, '8'), [6102, 73371]),
('control: large refund', (5000, 1000, 9000, '12.5'), [500, -4500]),
('control: half cent', (1001, 0, 0, '50'), [501, 1502]), ('control: no surtax', (4200, 100, 0, '0'), [0, 4100]),
('control: typical', (100000, 20000, 5000, '17.5'), [14000, 89000])],
[('regression surtax-base 1', (176644, 20000, 500, '8'), [12532, 168676]),
('regression surtax-base 2', (107676, 1000, 9000, '8'), [8534, 106210]),
('partial repair guard 1', (171795, 55836, 500, '1.5'), [1739, 117198]),
('partial repair guard 2', (195423, 1000, 9000, '17.5'), [34024, 219447]),
('control: typical', (100000, 20000, 5000, '17.5'), [14000, 89000]),
('control: credits exceed tax', (1000, 3000, 500, '20'), [0, -500]),
('control: rounding', (333, 0, 0, '1.5'), [5, 338]),
('control: large refund', (5000, 1000, 9000, '12.5'), [500, -4500])]]
for label, args, expected in cases[N - 1]:
check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| regression surtax-base 1 | [14000, 89000] | [14000, 89000] | Passed |
| regression surtax-base 2 | [0, -500] | [0, -500] | Passed |
| partial repair guard 2 | [500, -4500] | [500, -4500] | Passed |
| control: rounding | [5, 338] | [5, 338] | Passed |
| control: half cent | [501, 1502] | [501, 1502] | Passed |
| control: no surtax | [0, 4100] | [0, 4100] | Passed |
SHA-256 / 396edfdb804134d218ef5ebae16782c84d1355c6a43a26d3c4769357a0b513c6
Verification & scope
A deterministic, bounded teaching model with a stipulated toy contract; it makes no claim of conformance to any real regulation, standard, or institution's rules. 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.
Observations recorded using Python 3.12.14 at 2026-09-29T14:47:06.939203+00:00.
Case digest / e9ea5f6a65f313c779c8c7bcdbbf2edafb665712e64265be9e03eebd424af0c6