FA-62801 / Tax bracket computation / Open access

The surcharge takes the greater of the full rate and the gliding cap · case 01

High incomes pay 11.9% of the excess instead of 5.5% of the tax.

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

ROOT CAUSE

max() is used where the lesser of the two amounts is required.

VERIFIED REPAIR

Use min() of 5.5% of the tax and 11.9% of the excess.

Unsuccessful approach: Charging 5.5% of only the excess treats the exemption limit as an allowance.

Case contract

solve(income_tax, joint): stipulated surcharge on income tax, in integer cents. The exemption limit is 1813000 (doubled for joint assessment). At or below it the surcharge is 0; above it the surcharge is the lesser of 5.5% of the income tax and 11.9% of the excess over the limit (a gliding zone), rounded down to cents.

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(income_tax, joint):
    thr = 1813000 * (2 if joint else 1)
    if income_tax <= thr: return 0
    soli = max(income_tax * Fraction(55, 1000), (income_tax - thr) * Fraction(119, 1000))
    return int(soli)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('regression lesser-of 1', (5000000, False), 275000), ('regression lesser-of 2', (1900000, False), 10353),
  ('control: at limit', (1813000, False), 0), ('control: joint glide', (3700000, True), 8806),
  ('control: joint below', (3000000, True), 0), ('control: glide edge', (3300000, False), 176953)],
 [('regression lesser-of 1', (3700000, True), 8806), ('regression lesser-of 2', (3300000, False), 176953),
  ('control: joint below', (3000000, True), 0), ('control: at limit', (1813000, False), 0),
  ('control: gliding zone', (1900000, False), 10353), ('control: full rate', (5000000, False), 275000)],
 [('regression lesser-of 1', (3626001, False), 199430), ('regression lesser-of 2', (1813009, False), 1),
  ('control: at limit', (1813000, False), 0), ('control: gliding zone', (1900000, False), 10353),
  ('control: full rate', (5000000, False), 275000), ('control: joint glide', (3700000, True), 8806)],
 [('regression lesser-of 1', (1983210, False), 20254), ('regression lesser-of 2', (1813001, False), 0),
  ('partial repair guard 2', (4499538, True), 103951), ('control: joint glide', (3700000, True), 8806),
  ('control: joint below', (3000000, True), 0), ('control: glide edge', (3300000, False), 176953),
  ('control: at limit', (1813000, False), 0)],
 [('regression lesser-of 1', (3626001, True), 0), ('regression lesser-of 2', (4499538, True), 103951),
  ('partial repair guard 1', (3835420, False), 210948), ('partial repair guard 2', (3256603, False), 171788),
  ('control: at limit', (1813000, False), 0), ('control: gliding zone', (1900000, False), 10353),
  ('control: full rate', (5000000, False), 275000), ('control: joint glide', (3700000, True), 8806)]]
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 lesser-of 1	`379253`	`275000`	Failed
regression lesser-of 2	`104500`	`10353`	Failed
control: at limit	`0`	`0`	Passed
control: joint glide	`203500`	`8806`	Failed
control: joint below	`0`	`0`	Passed
control: glide edge	`181500`	`176953`	Failed

SHA-256 / 4e42a68242778f06eb6851bcf93c65b588e2e61ea8fd809c715fd6133ef55d95

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(income_tax, joint):
    thr = 1813000 * (2 if joint else 1)
    if income_tax <= thr: return 0
    soli = (income_tax - thr) * Fraction(55, 1000)
    return int(soli)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('regression lesser-of 1', (5000000, False), 275000), ('regression lesser-of 2', (1900000, False), 10353),
  ('control: at limit', (1813000, False), 0), ('control: joint glide', (3700000, True), 8806),
  ('control: joint below', (3000000, True), 0), ('control: glide edge', (3300000, False), 176953)],
 [('regression lesser-of 1', (3700000, True), 8806), ('regression lesser-of 2', (3300000, False), 176953),
  ('control: joint below', (3000000, True), 0), ('control: at limit', (1813000, False), 0),
  ('control: gliding zone', (1900000, False), 10353), ('control: full rate', (5000000, False), 275000)],
 [('regression lesser-of 1', (3626001, False), 199430), ('regression lesser-of 2', (1813009, False), 1),
  ('control: at limit', (1813000, False), 0), ('control: gliding zone', (1900000, False), 10353),
  ('control: full rate', (5000000, False), 275000), ('control: joint glide', (3700000, True), 8806)],
 [('regression lesser-of 1', (1983210, False), 20254), ('regression lesser-of 2', (1813001, False), 0),
  ('partial repair guard 2', (4499538, True), 103951), ('control: joint glide', (3700000, True), 8806),
  ('control: joint below', (3000000, True), 0), ('control: glide edge', (3300000, False), 176953),
  ('control: at limit', (1813000, False), 0)],
 [('regression lesser-of 1', (3626001, True), 0), ('regression lesser-of 2', (4499538, True), 103951),
  ('partial repair guard 1', (3835420, False), 210948), ('partial repair guard 2', (3256603, False), 171788),
  ('control: at limit', (1813000, False), 0), ('control: gliding zone', (1900000, False), 10353),
  ('control: full rate', (5000000, False), 275000), ('control: joint glide', (3700000, True), 8806)]]
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 lesser-of 1	`175285`	`275000`	Failed
regression lesser-of 2	`4785`	`10353`	Failed
control: at limit	`0`	`0`	Passed
control: joint glide	`4070`	`8806`	Failed
control: joint below	`0`	`0`	Passed
control: glide edge	`81785`	`176953`	Failed

SHA-256 / 4c5d533eb7e17cb2a028a096caea4b5e499f0d1b4c258b56ea9e3ca2c7de5c95

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(income_tax, joint):
    thr = 1813000 * (2 if joint else 1)
    if income_tax <= thr: return 0
    soli = min(income_tax * Fraction(55, 1000), (income_tax - thr) * Fraction(119, 1000))
    return int(soli)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('regression lesser-of 1', (5000000, False), 275000), ('regression lesser-of 2', (1900000, False), 10353),
  ('control: at limit', (1813000, False), 0), ('control: joint glide', (3700000, True), 8806),
  ('control: joint below', (3000000, True), 0), ('control: glide edge', (3300000, False), 176953)],
 [('regression lesser-of 1', (3700000, True), 8806), ('regression lesser-of 2', (3300000, False), 176953),
  ('control: joint below', (3000000, True), 0), ('control: at limit', (1813000, False), 0),
  ('control: gliding zone', (1900000, False), 10353), ('control: full rate', (5000000, False), 275000)],
 [('regression lesser-of 1', (3626001, False), 199430), ('regression lesser-of 2', (1813009, False), 1),
  ('control: at limit', (1813000, False), 0), ('control: gliding zone', (1900000, False), 10353),
  ('control: full rate', (5000000, False), 275000), ('control: joint glide', (3700000, True), 8806)],
 [('regression lesser-of 1', (1983210, False), 20254), ('regression lesser-of 2', (1813001, False), 0),
  ('partial repair guard 2', (4499538, True), 103951), ('control: joint glide', (3700000, True), 8806),
  ('control: joint below', (3000000, True), 0), ('control: glide edge', (3300000, False), 176953),
  ('control: at limit', (1813000, False), 0)],
 [('regression lesser-of 1', (3626001, True), 0), ('regression lesser-of 2', (4499538, True), 103951),
  ('partial repair guard 1', (3835420, False), 210948), ('partial repair guard 2', (3256603, False), 171788),
  ('control: at limit', (1813000, False), 0), ('control: gliding zone', (1900000, False), 10353),
  ('control: full rate', (5000000, False), 275000), ('control: joint glide', (3700000, True), 8806)]]
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 lesser-of 1	`275000`	`275000`	Passed
regression lesser-of 2	`10353`	`10353`	Passed
control: at limit	`0`	`0`	Passed
control: joint glide	`8806`	`8806`	Passed
control: joint below	`0`	`0`	Passed
control: glide edge	`176953`	`176953`	Passed

SHA-256 / fd894cbae7078c8209dea06daf261773002dd346028d091858af0cbab296efe3

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 2026-09-29T14:47:08.034132+00:00.

Case digest / c0bd9904c248fa46b32d41261ba812734416ac9f19ea3a602c73f9ea3d50f1d9