FA-62781 / Tax bracket computation / Open access
Excess investment income only trims the credit · case 01
Filers with investment income over the limit still receive most of the credit.
ROOT CAUSE
Investment income above the limit is subtracted from the credit instead of disqualifying it.
THE FAILURE
Investment income above the limit is subtracted from the credit instead of disqualifying it.
Unsuccessful approach: Disqualifying at 11600 exactly rejects filers who are at, not above, the limit.
Case contract
solve(earned, agi, children, mfj, invest): stipulated earned-income credit, whole dollars. Investment income above 11600 disqualifies (0). Parameters by min(children, 3): phase-in rate %, max credit, phase-out rate %, phase-out start (0: 7.65, 600, 7.65, 9800; 1: 34, 3995, 15.98, 21560; 2: 40, 6604, 21.06, 21560; 3+: 45, 7430, 21.06, 21560); joint filers add 6920 to the start. Credit = min(rate_in*earned, max) reduced by rate_out*(max(earned, agi) - start) when positive, floored at 0. Return integer cents half-up.
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(earned, agi, children, mfj, invest):
def prog(x, br):
tax, lower = Fraction(0), 0
for upper, rate in br:
top = x if upper is None else min(x, upper)
if top > lower: tax += (top - lower) * Fraction(rate) / 100
if upper is None or x <= upper: break
lower = upper
return tax
def cents(v):
v = v * 100
return int(v + Fraction(1, 2)) if v >= 0 else -int(-v + Fraction(1, 2))
P = {0: ['7.65', 7840, 600, '7.65', 9800], 1: ['34', 11750, 3995, '15.98', 21560], 2: ['40', 16510, 6604, '21.06', 21560], 3: ['45', 16510, 7430, '21.06', 21560]}
pass
rin, cap, mx, rout, start = P[min(children, 3)]
if mfj: start += 6920
credit = min(Fraction(rin) * earned / 100, Fraction(mx))
income = max(earned, agi)
if income > start: credit -= Fraction(rout) * (income - start) / 100
return cents(max(0, credit))
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('regression investment-disqualification 1', (20000, 20000, 1, False, 11601), 0),
('regression investment-disqualification 2', (5000, 28763, 3, False, 20000), 0),
('partial repair guard 1', (15000, 15000, 3, True, 11600), 675000),
('partial repair guard 2', (16510, 30000, 1, True, 11600), 375210),
('control: plateau', (10000, 10000, 1, False, 0), 340000),
('control: phase-out two children', (30000, 30000, 2, False, 0), 482654),
('control: agi drives phase-out', (12000, 30000, 1, False, 0), 264629),
('control: no children', (5000, 5000, 0, False, 0), 38250)],
[('regression investment-disqualification 1', (25000, 10000, 3, False, 11601), 0),
('regression investment-disqualification 2', (40000, 10000, 1, True, 20000), 0),
('partial repair guard 1', (5000, 0, 0, False, 11600), 38250),
('partial repair guard 2', (30678, 10000, 5, False, 11600), 550975),
('control: investment limit', (20000, 20000, 1, False, 11601), 0),
('control: no children', (5000, 5000, 0, False, 0), 38250), ('control: joint', (30000, 30000, 2, True, 0), 628389),
('control: four children', (15000, 15000, 4, False, 0), 675000)],
[('regression investment-disqualification 1', (10000, 0, 4, True, 20000), 0),
('regression investment-disqualification 2', (25000, 30000, 3, False, 11601), 0),
('partial repair guard 1', (40000, 10000, 5, True, 11600), 500389),
('partial repair guard 2', (5000, 30000, 2, False, 11600), 22254),
('control: four children', (15000, 15000, 4, False, 0), 675000),
('control: phased to zero', (60000, 60000, 1, False, 0), 0),
('control: investment at limit', (15000, 15000, 3, True, 11600), 675000),
('control: plateau', (10000, 10000, 1, False, 0), 340000)],
[('regression investment-disqualification 1', (5000, 30000, 4, False, 20000), 0),
('regression investment-disqualification 2', (5000, 4110, 0, False, 11601), 0),
('partial repair guard 1', (10000, 30000, 5, False, 11600), 272254),
('partial repair guard 2', (25000, 10000, 1, False, 11600), 344529),
('control: plateau', (10000, 10000, 1, False, 0), 340000),
('control: phase-out two children', (30000, 30000, 2, False, 0), 482654),
('control: agi drives phase-out', (12000, 30000, 1, False, 0), 264629),
('control: investment limit', (20000, 20000, 1, False, 11601), 0)],
[('regression investment-disqualification 1', (5000, 30000, 4, True, 11601), 0),
('regression investment-disqualification 2', (10000, 0, 5, True, 20000), 0),
('partial repair guard 1', (40000, 30000, 3, False, 11600), 354654),
('partial repair guard 2', (10000, 0, 5, True, 11600), 450000),
('control: investment limit', (20000, 20000, 1, False, 11601), 0),
('control: no children', (5000, 5000, 0, False, 0), 38250), ('control: joint', (30000, 30000, 2, True, 0), 628389),
('control: four children', (15000, 15000, 4, False, 0), 675000)]]
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 investment-disqualification 1 | 399500 | 0 | Failed |
| regression investment-disqualification 2 | 73305 | 0 | Failed |
| partial repair guard 1 | 675000 | 675000 | Passed |
| partial repair guard 2 | 375210 | 375210 | Passed |
| control: plateau | 340000 | 340000 | Passed |
| control: phase-out two children | 482654 | 482654 | Passed |
| control: agi drives phase-out | 264629 | 264629 | Passed |
| control: no children | 38250 | 38250 | Passed |
SHA-256 / 78ae7b01000b8dd8b958a179c3d695c7c6d3769d2cfa11b175bee86dcbb9dbec
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(earned, agi, children, mfj, invest):
def prog(x, br):
tax, lower = Fraction(0), 0
for upper, rate in br:
top = x if upper is None else min(x, upper)
if top > lower: tax += (top - lower) * Fraction(rate) / 100
if upper is None or x <= upper: break
lower = upper
return tax
def cents(v):
v = v * 100
return int(v + Fraction(1, 2)) if v >= 0 else -int(-v + Fraction(1, 2))
P = {0: ['7.65', 7840, 600, '7.65', 9800], 1: ['34', 11750, 3995, '15.98', 21560], 2: ['40', 16510, 6604, '21.06', 21560], 3: ['45', 16510, 7430, '21.06', 21560]}
if invest >= 11600: return 0
rin, cap, mx, rout, start = P[min(children, 3)]
if mfj: start += 6920
credit = min(Fraction(rin) * earned / 100, Fraction(mx))
income = max(earned, agi)
if income > start: credit -= Fraction(rout) * (income - start) / 100
return cents(max(0, credit))
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('regression investment-disqualification 1', (20000, 20000, 1, False, 11601), 0),
('regression investment-disqualification 2', (5000, 28763, 3, False, 20000), 0),
('partial repair guard 1', (15000, 15000, 3, True, 11600), 675000),
('partial repair guard 2', (16510, 30000, 1, True, 11600), 375210),
('control: plateau', (10000, 10000, 1, False, 0), 340000),
('control: phase-out two children', (30000, 30000, 2, False, 0), 482654),
('control: agi drives phase-out', (12000, 30000, 1, False, 0), 264629),
('control: no children', (5000, 5000, 0, False, 0), 38250)],
[('regression investment-disqualification 1', (25000, 10000, 3, False, 11601), 0),
('regression investment-disqualification 2', (40000, 10000, 1, True, 20000), 0),
('partial repair guard 1', (5000, 0, 0, False, 11600), 38250),
('partial repair guard 2', (30678, 10000, 5, False, 11600), 550975),
('control: investment limit', (20000, 20000, 1, False, 11601), 0),
('control: no children', (5000, 5000, 0, False, 0), 38250), ('control: joint', (30000, 30000, 2, True, 0), 628389),
('control: four children', (15000, 15000, 4, False, 0), 675000)],
[('regression investment-disqualification 1', (10000, 0, 4, True, 20000), 0),
('regression investment-disqualification 2', (25000, 30000, 3, False, 11601), 0),
('partial repair guard 1', (40000, 10000, 5, True, 11600), 500389),
('partial repair guard 2', (5000, 30000, 2, False, 11600), 22254),
('control: four children', (15000, 15000, 4, False, 0), 675000),
('control: phased to zero', (60000, 60000, 1, False, 0), 0),
('control: investment at limit', (15000, 15000, 3, True, 11600), 675000),
('control: plateau', (10000, 10000, 1, False, 0), 340000)],
[('regression investment-disqualification 1', (5000, 30000, 4, False, 20000), 0),
('regression investment-disqualification 2', (5000, 4110, 0, False, 11601), 0),
('partial repair guard 1', (10000, 30000, 5, False, 11600), 272254),
('partial repair guard 2', (25000, 10000, 1, False, 11600), 344529),
('control: plateau', (10000, 10000, 1, False, 0), 340000),
('control: phase-out two children', (30000, 30000, 2, False, 0), 482654),
('control: agi drives phase-out', (12000, 30000, 1, False, 0), 264629),
('control: investment limit', (20000, 20000, 1, False, 11601), 0)],
[('regression investment-disqualification 1', (5000, 30000, 4, True, 11601), 0),
('regression investment-disqualification 2', (10000, 0, 5, True, 20000), 0),
('partial repair guard 1', (40000, 30000, 3, False, 11600), 354654),
('partial repair guard 2', (10000, 0, 5, True, 11600), 450000),
('control: investment limit', (20000, 20000, 1, False, 11601), 0),
('control: no children', (5000, 5000, 0, False, 0), 38250), ('control: joint', (30000, 30000, 2, True, 0), 628389),
('control: four children', (15000, 15000, 4, False, 0), 675000)]]
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 investment-disqualification 1 | 0 | 0 | Passed |
| regression investment-disqualification 2 | 0 | 0 | Passed |
| partial repair guard 1 | 0 | 675000 | Failed |
| partial repair guard 2 | 0 | 375210 | Failed |
| control: plateau | 340000 | 340000 | Passed |
| control: phase-out two children | 482654 | 482654 | Passed |
| control: agi drives phase-out | 264629 | 264629 | Passed |
| control: no children | 38250 | 38250 | Passed |
SHA-256 / 72fc463933536c3b95245cbd30b87c1ff3a78ae7fbe1e1e6856f472803323a77
HELD IN THE MEMBER ARCHIVE
The verified repair and its recorded checks are member-only.
This mechanism has 8 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.
Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.
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Sign in to the archive ↗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 2026-09-29T14:47:07.987971+00:00.
Case digest / 80e8a93e8b0c88f57f7e1e3f01967db75ae7feb2a9a2e544f362557799eac7a9