FA-84626 / Betting odds conversion / Open access
Traditional display picks the next shorter fraction · case 01
A 3.40 price displays as 9/4 instead of 5/2.
ROOT CAUSE
The scan keeps the largest ladder fraction not above the target instead of the nearest.
VERIFIED REPAIR
Choose the ladder entry with the smallest absolute distance.
Unsuccessful approach: Taking the first ladder entry at or above the target always rounds toward the longer price.
Case contract
Display a decimal price (> 1, else "invalid") as the nearest traditional fraction from the ascending ladder ['1/10', '1/8', '1/5', '2/9', '1/4', '2/7', '1/3', '4/11', '2/5', '4/9', '1/2', '8/15', '4/7', '8/13', '4/6', '8/11', '4/5', '5/6', '10/11', 'evens', '11/10', '6/5', '5/4', '11/8', '6/4', '13/8', '7/4', '15/8', '2/1', '9/4', '5/2', '11/4', '3/1', '10/3', '7/2', '4/1', '9/2', '5/1', '11/2', '6/1', '13/2', '7/1', '15/2', '8/1', '17/2', '9/1', '10/1', '11/1', '12/1', '14/1', '16/1', '18/1', '20/1', '25/1', '33/1', '40/1', '50/1', '66/1', '100/1']. Distance is |fraction value - (d - 1)| with "evens" = 1; ties go to the earlier (shorter) ladder entry. Return the ladder string.
Why this case matters
UK-facing sites display decimal model prices as familiar traditional fractions.
1 / The failure
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
from fractions import Fraction
N = 1
observations = []
def solve(decimal):
LADDER = ['1/10', '1/8', '1/5', '2/9', '1/4', '2/7', '1/3', '4/11', '2/5', '4/9', '1/2', '8/15', '4/7', '8/13', '4/6', '8/11', '4/5', '5/6', '10/11', 'evens', '11/10', '6/5', '5/4', '11/8', '6/4', '13/8', '7/4', '15/8', '2/1', '9/4', '5/2', '11/4', '3/1', '10/3', '7/2', '4/1', '9/2', '5/1', '11/2', '6/1', '13/2', '7/1', '15/2', '8/1', '17/2', '9/1', '10/1', '11/1', '12/1', '14/1', '16/1', '18/1', '20/1', '25/1', '33/1', '40/1', '50/1', '66/1', '100/1']
def val(s):
return Fraction(1) if s == 'evens' else Fraction(s)
d = Fraction(decimal)
if d <= 1:
return 'invalid'
target = d - 1
best = None
for s in LADDER:
dist = abs(val(s) - target)
if best is None or val(s) <= target:
best = (dist, s)
return best[1]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
def run(args):
try:
return solve(*args)
except Exception as exc:
return 'raised ' + type(exc).__name__
cases = [[('control exact fraction', ('3.50',), '5/2'),
('control evens', ('2.00',), 'evens'),
('boundary odds-on', ('1.67',), '4/6'),
('boundary midpoint tie', ('3.875',), '11/4'),
('control long shot', ('120.0',), '100/1'),
('boundary no-profit price', ('1.00',), 'invalid'),
('regression: nearest versus floor', ('1.95',), '10/11'),
('regression: nearest versus floor', ('2.70',), '7/4'),
('variant scenario 1', ('1.50',), '1/2'),
('variant scenario 2', ('2.125',), '11/10')],
[('control exact fraction', ('3.50',), '5/2'),
('control evens', ('2.00',), 'evens'),
('boundary odds-on', ('1.67',), '4/6'),
('boundary midpoint tie', ('3.875',), '11/4'),
('control long shot', ('120.0',), '100/1'),
('boundary no-profit price', ('1.00',), 'invalid'),
('regression: nearest versus floor', ('1.95',), '10/11'),
('regression: nearest versus floor', ('1.48',), '1/2'),
('variant scenario 1', ('2.125',), '11/10'),
('variant scenario 2', ('3.875',), '11/4')],
[('control exact fraction', ('3.50',), '5/2'),
('control evens', ('2.00',), 'evens'),
('boundary odds-on', ('1.67',), '4/6'),
('boundary midpoint tie', ('3.875',), '11/4'),
('control long shot', ('120.0',), '100/1'),
('boundary no-profit price', ('1.00',), 'invalid'),
('regression: nearest versus floor', ('3.875',), '11/4'),
('regression: nearest versus floor', ('3.703',), '11/4'),
('variant scenario 1', ('1.118',), '1/8'),
('variant scenario 2', ('2.29',), '5/4')],
[('control exact fraction', ('3.50',), '5/2'),
('control evens', ('2.00',), 'evens'),
('boundary odds-on', ('1.67',), '4/6'),
('boundary midpoint tie', ('3.875',), '11/4'),
('control long shot', ('120.0',), '100/1'),
('boundary no-profit price', ('1.00',), 'invalid'),
('regression: nearest versus floor', ('6.79',), '6/1'),
('regression: nearest versus floor', ('3.875',), '11/4'),
('variant scenario 1', ('12.1',), '11/1'),
('variant scenario 2', ('93.4',), '100/1')],
[('control exact fraction', ('3.50',), '5/2'),
('control evens', ('2.00',), 'evens'),
('boundary odds-on', ('1.67',), '4/6'),
('boundary midpoint tie', ('3.875',), '11/4'),
('control long shot', ('120.0',), '100/1'),
('boundary no-profit price', ('1.00',), 'invalid'),
('regression: nearest versus floor', ('1.95',), '10/11'),
('regression: nearest versus floor', ('61.2',), '66/1'),
('variant scenario 1', ('3.875',), '11/4'),
('variant scenario 2', ('2.125',), '11/10')]]
for label, args, expected in cases[N - 1]:
check(label, run(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 |
|---|---|---|---|
| control exact fraction | 5/2 | 5/2 | Passed |
| control evens | evens | evens | Passed |
| boundary odds-on | 4/6 | 4/6 | Passed |
| boundary midpoint tie | 11/4 | 11/4 | Passed |
| control long shot | 100/1 | 100/1 | Passed |
| boundary no-profit price | invalid | invalid | Passed |
| regression: nearest versus floor | 10/11 | 10/11 | Passed |
| regression: nearest versus floor | 13/8 | 7/4 | Failed |
| variant scenario 1 | 1/2 | 1/2 | Passed |
| variant scenario 2 | 11/10 | 11/10 | Passed |
SHA-256 / 8a5b3a9061355625b047617d2df48aca68d2234c1e13da074e703b776e74f3a4
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(decimal):
LADDER = ['1/10', '1/8', '1/5', '2/9', '1/4', '2/7', '1/3', '4/11', '2/5', '4/9', '1/2', '8/15', '4/7', '8/13', '4/6', '8/11', '4/5', '5/6', '10/11', 'evens', '11/10', '6/5', '5/4', '11/8', '6/4', '13/8', '7/4', '15/8', '2/1', '9/4', '5/2', '11/4', '3/1', '10/3', '7/2', '4/1', '9/2', '5/1', '11/2', '6/1', '13/2', '7/1', '15/2', '8/1', '17/2', '9/1', '10/1', '11/1', '12/1', '14/1', '16/1', '18/1', '20/1', '25/1', '33/1', '40/1', '50/1', '66/1', '100/1']
def val(s):
return Fraction(1) if s == 'evens' else Fraction(s)
d = Fraction(decimal)
if d <= 1:
return 'invalid'
target = d - 1
best = None
for s in LADDER:
dist = abs(val(s) - target)
if best is None or (val(s) >= target and best[0] != 0 and val(best[1]) < target):
best = (dist, s)
return best[1]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
def run(args):
try:
return solve(*args)
except Exception as exc:
return 'raised ' + type(exc).__name__
cases = [[('control exact fraction', ('3.50',), '5/2'),
('control evens', ('2.00',), 'evens'),
('boundary odds-on', ('1.67',), '4/6'),
('boundary midpoint tie', ('3.875',), '11/4'),
('control long shot', ('120.0',), '100/1'),
('boundary no-profit price', ('1.00',), 'invalid'),
('regression: nearest versus floor', ('1.95',), '10/11'),
('regression: nearest versus floor', ('2.70',), '7/4'),
('variant scenario 1', ('1.50',), '1/2'),
('variant scenario 2', ('2.125',), '11/10')],
[('control exact fraction', ('3.50',), '5/2'),
('control evens', ('2.00',), 'evens'),
('boundary odds-on', ('1.67',), '4/6'),
('boundary midpoint tie', ('3.875',), '11/4'),
('control long shot', ('120.0',), '100/1'),
('boundary no-profit price', ('1.00',), 'invalid'),
('regression: nearest versus floor', ('1.95',), '10/11'),
('regression: nearest versus floor', ('1.48',), '1/2'),
('variant scenario 1', ('2.125',), '11/10'),
('variant scenario 2', ('3.875',), '11/4')],
[('control exact fraction', ('3.50',), '5/2'),
('control evens', ('2.00',), 'evens'),
('boundary odds-on', ('1.67',), '4/6'),
('boundary midpoint tie', ('3.875',), '11/4'),
('control long shot', ('120.0',), '100/1'),
('boundary no-profit price', ('1.00',), 'invalid'),
('regression: nearest versus floor', ('3.875',), '11/4'),
('regression: nearest versus floor', ('3.703',), '11/4'),
('variant scenario 1', ('1.118',), '1/8'),
('variant scenario 2', ('2.29',), '5/4')],
[('control exact fraction', ('3.50',), '5/2'),
('control evens', ('2.00',), 'evens'),
('boundary odds-on', ('1.67',), '4/6'),
('boundary midpoint tie', ('3.875',), '11/4'),
('control long shot', ('120.0',), '100/1'),
('boundary no-profit price', ('1.00',), 'invalid'),
('regression: nearest versus floor', ('6.79',), '6/1'),
('regression: nearest versus floor', ('3.875',), '11/4'),
('variant scenario 1', ('12.1',), '11/1'),
('variant scenario 2', ('93.4',), '100/1')],
[('control exact fraction', ('3.50',), '5/2'),
('control evens', ('2.00',), 'evens'),
('boundary odds-on', ('1.67',), '4/6'),
('boundary midpoint tie', ('3.875',), '11/4'),
('control long shot', ('120.0',), '100/1'),
('boundary no-profit price', ('1.00',), 'invalid'),
('regression: nearest versus floor', ('1.95',), '10/11'),
('regression: nearest versus floor', ('61.2',), '66/1'),
('variant scenario 1', ('3.875',), '11/4'),
('variant scenario 2', ('2.125',), '11/10')]]
for label, args, expected in cases[N - 1]:
check(label, run(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 |
|---|---|---|---|
| control exact fraction | 5/2 | 5/2 | Passed |
| control evens | evens | evens | Passed |
| boundary odds-on | 8/11 | 4/6 | Failed |
| boundary midpoint tie | 3/1 | 11/4 | Failed |
| control long shot | 1/10 | 100/1 | Failed |
| boundary no-profit price | invalid | invalid | Passed |
| regression: nearest versus floor | evens | 10/11 | Failed |
| regression: nearest versus floor | 7/4 | 7/4 | Passed |
| variant scenario 1 | 1/2 | 1/2 | Passed |
| variant scenario 2 | 6/5 | 11/10 | Failed |
SHA-256 / 6043dffbfb03195406eb171713851a0d0cfde92cde3c4b0ba42408934d9d9119
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(decimal):
LADDER = ['1/10', '1/8', '1/5', '2/9', '1/4', '2/7', '1/3', '4/11', '2/5', '4/9', '1/2', '8/15', '4/7', '8/13', '4/6', '8/11', '4/5', '5/6', '10/11', 'evens', '11/10', '6/5', '5/4', '11/8', '6/4', '13/8', '7/4', '15/8', '2/1', '9/4', '5/2', '11/4', '3/1', '10/3', '7/2', '4/1', '9/2', '5/1', '11/2', '6/1', '13/2', '7/1', '15/2', '8/1', '17/2', '9/1', '10/1', '11/1', '12/1', '14/1', '16/1', '18/1', '20/1', '25/1', '33/1', '40/1', '50/1', '66/1', '100/1']
def val(s):
return Fraction(1) if s == 'evens' else Fraction(s)
d = Fraction(decimal)
if d <= 1:
return 'invalid'
target = d - 1
best = None
for s in LADDER:
dist = abs(val(s) - target)
if best is None or dist < best[0]:
best = (dist, s)
return best[1]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
def run(args):
try:
return solve(*args)
except Exception as exc:
return 'raised ' + type(exc).__name__
cases = [[('control exact fraction', ('3.50',), '5/2'),
('control evens', ('2.00',), 'evens'),
('boundary odds-on', ('1.67',), '4/6'),
('boundary midpoint tie', ('3.875',), '11/4'),
('control long shot', ('120.0',), '100/1'),
('boundary no-profit price', ('1.00',), 'invalid'),
('regression: nearest versus floor', ('1.95',), '10/11'),
('regression: nearest versus floor', ('2.70',), '7/4'),
('variant scenario 1', ('1.50',), '1/2'),
('variant scenario 2', ('2.125',), '11/10')],
[('control exact fraction', ('3.50',), '5/2'),
('control evens', ('2.00',), 'evens'),
('boundary odds-on', ('1.67',), '4/6'),
('boundary midpoint tie', ('3.875',), '11/4'),
('control long shot', ('120.0',), '100/1'),
('boundary no-profit price', ('1.00',), 'invalid'),
('regression: nearest versus floor', ('1.95',), '10/11'),
('regression: nearest versus floor', ('1.48',), '1/2'),
('variant scenario 1', ('2.125',), '11/10'),
('variant scenario 2', ('3.875',), '11/4')],
[('control exact fraction', ('3.50',), '5/2'),
('control evens', ('2.00',), 'evens'),
('boundary odds-on', ('1.67',), '4/6'),
('boundary midpoint tie', ('3.875',), '11/4'),
('control long shot', ('120.0',), '100/1'),
('boundary no-profit price', ('1.00',), 'invalid'),
('regression: nearest versus floor', ('3.875',), '11/4'),
('regression: nearest versus floor', ('3.703',), '11/4'),
('variant scenario 1', ('1.118',), '1/8'),
('variant scenario 2', ('2.29',), '5/4')],
[('control exact fraction', ('3.50',), '5/2'),
('control evens', ('2.00',), 'evens'),
('boundary odds-on', ('1.67',), '4/6'),
('boundary midpoint tie', ('3.875',), '11/4'),
('control long shot', ('120.0',), '100/1'),
('boundary no-profit price', ('1.00',), 'invalid'),
('regression: nearest versus floor', ('6.79',), '6/1'),
('regression: nearest versus floor', ('3.875',), '11/4'),
('variant scenario 1', ('12.1',), '11/1'),
('variant scenario 2', ('93.4',), '100/1')],
[('control exact fraction', ('3.50',), '5/2'),
('control evens', ('2.00',), 'evens'),
('boundary odds-on', ('1.67',), '4/6'),
('boundary midpoint tie', ('3.875',), '11/4'),
('control long shot', ('120.0',), '100/1'),
('boundary no-profit price', ('1.00',), 'invalid'),
('regression: nearest versus floor', ('1.95',), '10/11'),
('regression: nearest versus floor', ('61.2',), '66/1'),
('variant scenario 1', ('3.875',), '11/4'),
('variant scenario 2', ('2.125',), '11/10')]]
for label, args, expected in cases[N - 1]:
check(label, run(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 |
|---|---|---|---|
| control exact fraction | 5/2 | 5/2 | Passed |
| control evens | evens | evens | Passed |
| boundary odds-on | 4/6 | 4/6 | Passed |
| boundary midpoint tie | 11/4 | 11/4 | Passed |
| control long shot | 100/1 | 100/1 | Passed |
| boundary no-profit price | invalid | invalid | Passed |
| regression: nearest versus floor | 10/11 | 10/11 | Passed |
| regression: nearest versus floor | 7/4 | 7/4 | Passed |
| variant scenario 1 | 1/2 | 1/2 | Passed |
| variant scenario 2 | 11/10 | 11/10 | Passed |
SHA-256 / 67aca8dad3e6e503a251e6224d876009ad96794efc6fd7808b0489377fd37b8b
Verification & scope
Stipulated, bounded toy contract stated in the contract field; not a claim of conformance with any operator, exchange or regulator rule set. 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 2026-09-29T14:50:32.612649+00:00.
Case digest / ad1874deda46b07848922f3b15c4c2846b2a42bdc3a3db69501317b350bef789