FA-5801 / Planar geometry / Open access

Annulus area divided by pi · case 01

Squaring the thickness ignores the annulus mean radius.

Verified by executionVariant 1 · 4 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Squaring the thickness ignores the annulus mean radius.

THE FAILURE

Squaring the thickness ignores the annulus mean radius.

Unsuccessful approach: The hole area is added rather than removed.

Case contract

Integer coordinates and lengths, with exact arithmetic except for indicated division results. Lengths are nonnegative. Rectangles are (xmin,ymin,xmax,ymax) with ordered bounds; coordinate vectors have matching dimensions. Annulus area divided by pi. Exact operational definition: outer**2-inner**2

Why this case matters

Small exact fixtures expose this error without platform timing, external services, or probabilistic observations. Planar geometry results depend on the stated convention.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import math
import calendar
import statistics
import itertools
from fractions import Fraction
from datetime import date, datetime, timedelta, timezone
from decimal import Decimal, ROUND_HALF_UP, ROUND_DOWN, ROUND_CEILING, ROUND_FLOOR

N = 1
observations = []
def solve(outer, inner):
    return (outer-inner)**2
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1: (5, 3)', solve(*(5, 3)), 16)
check('fixture 2: (3, 3)', solve(*(3, 3)), 0)
check('fixture 3: (4, 0)', solve(*(4, 0)), 16)
check('fixture 4: (2, 1)', solve(*(2, 1)), 3)
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
fixture 1: (5, 3)	`4`	`16`	Failed
fixture 2: (3, 3)	`0`	`0`	Passed
fixture 3: (4, 0)	`16`	`16`	Passed
fixture 4: (2, 1)	`1`	`3`	Failed

SHA-256 / c8aedfd7fa91067b306f7243a09511f6ad8782c8a973b6a511807b80aca276ca

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import math
import calendar
import statistics
import itertools
from fractions import Fraction
from datetime import date, datetime, timedelta, timezone
from decimal import Decimal, ROUND_HALF_UP, ROUND_DOWN, ROUND_CEILING, ROUND_FLOOR

N = 1
observations = []
def solve(outer, inner):
    return outer**2+inner**2
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1: (5, 3)', solve(*(5, 3)), 16)
check('fixture 2: (3, 3)', solve(*(3, 3)), 0)
check('fixture 3: (4, 0)', solve(*(4, 0)), 16)
check('fixture 4: (2, 1)', solve(*(2, 1)), 3)
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
fixture 1: (5, 3)	`34`	`16`	Failed
fixture 2: (3, 3)	`18`	`0`	Failed
fixture 3: (4, 0)	`16`	`16`	Passed
fixture 4: (2, 1)	`5`	`3`	Failed

SHA-256 / 66f26b33f2eee5d41f80881c1f4f37972ff102b4c6a77633bd09de891c2bc7cf

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 4 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.

Member access is invitation-based. Sign in with your invited account to inspect the repair.

Verification & scope

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 2026-09-29T14:37:53.689165+00:00.

Case digest / 4cc64ad1e3eba71be6c3dc71efe5898eb1aab73d1ad66b7ab0af984e50c4db09