FAILURE MAP
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FA-62691 / Tax bracket computation / Open access

Excess nonrefundable credits make the surtax negative · case 01

Credits larger than the state tax produce a negative local surtax and an extra refund.

Verified by executionVariant 1 · 6 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

State tax after nonrefundable credits is not floored at zero.

VERIFIED REPAIR

Floor state tax after nonrefundable credits at zero.

Unsuccessful approach: Flooring only the local surtax still lets the negative credited state tax create a refund.

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 = 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 credited-floor 1', (1000, 3000, 500, '20'), [0, -500]),
  ('regression credited-floor 2', (18157, 72365, 10702, '3.25'), [0, -10702]),
  ('control: typical', (100000, 20000, 5000, '17.5'), [14000, 89000]),
  ('control: rounding', (333, 0, 0, '1.5'), [5, 338]),
  ('control: large refund', (5000, 1000, 9000, '12.5'), [500, -4500]),
  ('control: half cent', (1001, 0, 0, '50'), [501, 1502])],
 [('regression credited-floor 1', (60634, 89812, 9000, '12.5'), [0, -9000]),
  ('regression credited-floor 2', (7099, 20000, 500, '20'), [0, -500]),
  ('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 credited-floor 1', (44659, 45143, 0, '1.5'), [0, 0]),
  ('regression credited-floor 2', (63135, 85065, 500, '20'), [0, -500]),
  ('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 credited-floor 1', (5225, 20000, 9000, '8'), [0, -9000]),
  ('regression credited-floor 2', (18855, 20000, 500, '50'), [0, -500]),
  ('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 credited-floor 1', (56595, 97017, 0, '1.5'), [0, 0]),
  ('regression credited-floor 2', (27017, 95158, 26974, '20'), [0, -26974]),
  ('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 fixtureActualExpectedOutcome
regression credited-floor 1[-399, -2899][0, -500]Failed
regression credited-floor 2[-1761, -66671][0, -10702]Failed
control: typical[14000, 89000][14000, 89000]Passed
control: rounding[5, 338][5, 338]Passed
control: large refund[500, -4500][500, -4500]Passed
control: half cent[501, 1502][501, 1502]Passed

SHA-256 / bed80bf8c6334e8bccf345cc17eb9a519c3ac3f28c02ddd4eab9f6ea188554cc

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 = state - nonref
    local = max(0, 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 credited-floor 1', (1000, 3000, 500, '20'), [0, -500]),
  ('regression credited-floor 2', (18157, 72365, 10702, '3.25'), [0, -10702]),
  ('control: typical', (100000, 20000, 5000, '17.5'), [14000, 89000]),
  ('control: rounding', (333, 0, 0, '1.5'), [5, 338]),
  ('control: large refund', (5000, 1000, 9000, '12.5'), [500, -4500]),
  ('control: half cent', (1001, 0, 0, '50'), [501, 1502])],
 [('regression credited-floor 1', (60634, 89812, 9000, '12.5'), [0, -9000]),
  ('regression credited-floor 2', (7099, 20000, 500, '20'), [0, -500]),
  ('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 credited-floor 1', (44659, 45143, 0, '1.5'), [0, 0]),
  ('regression credited-floor 2', (63135, 85065, 500, '20'), [0, -500]),
  ('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 credited-floor 1', (5225, 20000, 9000, '8'), [0, -9000]),
  ('regression credited-floor 2', (18855, 20000, 500, '50'), [0, -500]),
  ('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 credited-floor 1', (56595, 97017, 0, '1.5'), [0, 0]),
  ('regression credited-floor 2', (27017, 95158, 26974, '20'), [0, -26974]),
  ('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 fixtureActualExpectedOutcome
regression credited-floor 1[0, -2500][0, -500]Failed
regression credited-floor 2[0, -64910][0, -10702]Failed
control: typical[14000, 89000][14000, 89000]Passed
control: rounding[5, 338][5, 338]Passed
control: large refund[500, -4500][500, -4500]Passed
control: half cent[501, 1502][501, 1502]Passed

SHA-256 / eec3b473cc7465a887be8389418aff425502de433dce89dc023efd788a338a07

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 credited-floor 1', (1000, 3000, 500, '20'), [0, -500]),
  ('regression credited-floor 2', (18157, 72365, 10702, '3.25'), [0, -10702]),
  ('control: typical', (100000, 20000, 5000, '17.5'), [14000, 89000]),
  ('control: rounding', (333, 0, 0, '1.5'), [5, 338]),
  ('control: large refund', (5000, 1000, 9000, '12.5'), [500, -4500]),
  ('control: half cent', (1001, 0, 0, '50'), [501, 1502])],
 [('regression credited-floor 1', (60634, 89812, 9000, '12.5'), [0, -9000]),
  ('regression credited-floor 2', (7099, 20000, 500, '20'), [0, -500]),
  ('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 credited-floor 1', (44659, 45143, 0, '1.5'), [0, 0]),
  ('regression credited-floor 2', (63135, 85065, 500, '20'), [0, -500]),
  ('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 credited-floor 1', (5225, 20000, 9000, '8'), [0, -9000]),
  ('regression credited-floor 2', (18855, 20000, 500, '50'), [0, -500]),
  ('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 credited-floor 1', (56595, 97017, 0, '1.5'), [0, 0]),
  ('regression credited-floor 2', (27017, 95158, 26974, '20'), [0, -26974]),
  ('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 fixtureActualExpectedOutcome
regression credited-floor 1[0, -500][0, -500]Passed
regression credited-floor 2[0, -10702][0, -10702]Passed
control: typical[14000, 89000][14000, 89000]Passed
control: rounding[5, 338][5, 338]Passed
control: large refund[500, -4500][500, -4500]Passed
control: half cent[501, 1502][501, 1502]Passed

SHA-256 / 9255baa640452bacfd33fabc7cbb3086be4314fb3f532c5617f835b70abfe115

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 2026-09-29T14:47:07.032365+00:00.

Case digest / e30101493eb445e662c037347ddef922244a24824878cd9b5281fc8791a8f064