FA-61211 / Bond day-count conventions / Open access

Settlement date from a business-day lag across two calendars: the trade date counts as the first business day · case 01

Settlement is one business day early.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The loop tests the current day before advancing, so the trade date is counted.

VERIFIED REPAIR

Advance first, then count business days strictly after the trade date.

Unsuccessful approach: Skipping the trade date but still advancing after counting returns the day after the n-th business day.

Case contract

Inputs a trade date (a business day), a lag n and two holiday lists. A business day is a weekday that is a holiday in neither calendar. Settlement is the n-th business day strictly after trade (trade date for n=0). Return [y,m,d].

Why this case matters

Bond accrual and pricing systems depend on exact day-count arithmetic; a single-day error changes settlement cash.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import datetime
N = 1
observations = []
def solve(trade, n, hol_a, hol_b):
    T = datetime.date(*trade)
    HA = {datetime.date(*h) for h in hol_a}
    HB = {datetime.date(*h) for h in hol_b}
    def biz(x):
        return x.weekday() < 5 and x not in HA and x not in HB
    x = T
    k = 0
    while k < n:
        if biz(x):
            k += 1
        if k < n:
            x += datetime.timedelta(days=1)
    return [x.year, x.month, x.day]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression trade date counted 1', [[2028, 3, 31], 5, [[2028, 4, 3], [2028, 4, 6]], [[2028, 4, 4], [2028, 4, 7]]], [2028, 4, 13]], ['regression trade date counted 2', [[2027, 8, 5], 2, [], [[2027, 8, 7]]], [2027, 8, 9]], ['partial repair probe 1', [[2027, 9, 30], 2, [], [[2027, 10, 3]]], [2027, 10, 4]], ['partial repair probe 2', [[2021, 1, 18], 2, [[2021, 1, 27]], [[2021, 1, 27], [2021, 1, 19]]], [2021, 1, 21]], ['boundary control 1', [[2024, 5, 3], 0, [], []], [2024, 5, 3]], ['normal control 1', [[2029, 3, 5], 0, [], [[2029, 3, 8], [2029, 3, 13]]], [2029, 3, 5]], ['normal control 2', [[2020, 6, 30], 0, [], []], [2020, 6, 30]], ['normal control 3', [[2022, 7, 21], 0, [[2022, 7, 30], [2022, 7, 25]], []], [2022, 7, 21]]], [['regression trade date counted 1', [[2030, 2, 28], 2, [], [[2030, 3, 4], [2030, 3, 1]]], [2030, 3, 6]], ['regression trade date counted 2', [[2027, 2, 5], 1, [[2027, 2, 10]], [[2027, 2, 13], [2027, 2, 8]]], [2027, 2, 9]], ['partial repair probe 1', [[2019, 5, 31], 3, [[2019, 6, 8]], []], [2019, 6, 5]], ['partial repair probe 2', [[2024, 7, 31], 1, [], [[2024, 8, 9], [2024, 8, 4]]], [2024, 8, 1]], ['boundary control 1', [[2024, 5, 3], 0, [], []], [2024, 5, 3]], ['normal control 1', [[2020, 2, 28], 0, [[2020, 3, 1]], []], [2020, 2, 28]], ['normal control 2', [[2024, 4, 22], 0, [], []], [2024, 4, 22]], ['normal control 3', [[2021, 1, 25], 0, [[2021, 2, 3], [2021, 2, 1]], [[2021, 1, 29], [2021, 1, 30]]], [2021, 1, 25]]], [['regression trade date counted 1', [[2027, 7, 21], 2, [[2027, 7, 23], [2027, 7, 30]], [[2027, 7, 28], [2027, 7, 26]]], [2027, 7, 27]], ['regression trade date counted 2', [[2026, 6, 30], 1, [[2026, 7, 1], [2026, 7, 6]], [[2026, 7, 2], [2026, 7, 5]]], [2026, 7, 3]], ['partial repair probe 1', [[2021, 10, 15], 3, [], [[2021, 10, 24]]], [2021, 10, 20]], ['partial repair probe 2', [[2025, 10, 31], 2, [[2025, 11, 1]], [[2025, 11, 9]]], [2025, 11, 4]], ['boundary control 1', [[2024, 5, 3], 0, [], []], [2024, 5, 3]], ['normal control 1', [[2022, 1, 21], 0, [[2022, 1, 23], [2022, 1, 22]], [[2022, 1, 26], [2022, 1, 29]]], [2022, 1, 21]], ['normal control 2', [[2025, 9, 22], 0, [[2025, 9, 26]], [[2025, 9, 27], [2025, 9, 26]]], [2025, 9, 22]], ['normal control 3', [[2023, 2, 28], 0, [[2023, 3, 8]], [[2023, 3, 4]]], [2023, 2, 28]]], [['regression trade date counted 1', [[2019, 7, 31], 2, [[2019, 8, 2]], []], [2019, 8, 5]], ['regression trade date counted 2', [[2026, 1, 5], 2, [], [[2026, 1, 11]]], [2026, 1, 7]], ['partial repair probe 1', [[2030, 5, 31], 3, [[2030, 6, 2]], []], [2030, 6, 5]], ['partial repair probe 2', [[2023, 10, 31], 2, [[2023, 11, 7], [2023, 11, 2]], [[2023, 11, 3], [2023, 11, 2]]], [2023, 11, 6]], ['boundary control 1', [[2024, 5, 3], 0, [], []], [2024, 5, 3]], ['normal control 1', [[2020, 4, 30], 0, [[2020, 5, 7]], [[2020, 5, 5], [2020, 5, 1]]], [2020, 4, 30]], ['normal control 2', [[2019, 8, 6], 0, [[2019, 8, 12]], []], [2019, 8, 6]], ['normal control 3', [[2019, 7, 31], 0, [], []], [2019, 7, 31]]], [['regression trade date counted 1', [[2026, 12, 31], 2, [], []], [2027, 1, 4]], ['regression trade date counted 2', [[2026, 11, 9], 2, [[2026, 11, 16]], [[2026, 11, 18], [2026, 11, 12]]], [2026, 11, 11]], ['partial repair probe 1', [[2019, 7, 1], 5, [], []], [2019, 7, 8]], ['partial repair probe 2', [[2029, 5, 28], 2, [], [[2029, 6, 1]]], [2029, 5, 30]], ['boundary control 1', [[2024, 5, 3], 0, [], []], [2024, 5, 3]], ['normal control 1', [[2025, 6, 2], 0, [[2025, 6, 8]], [[2025, 6, 5], [2025, 6, 9]]], [2025, 6, 2]], ['normal control 2', [[2021, 9, 10], 0, [], [[2021, 9, 19]]], [2021, 9, 10]], ['normal control 3', [[2020, 10, 26], 0, [[2020, 10, 28], [2020, 10, 31]], [[2020, 11, 3], [2020, 11, 4]]], [2020, 10, 26]]]]
for label, args, expected in fixtures[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 trade date counted 1	`[2028, 4, 12]`	`[2028, 4, 13]`	Failed
regression trade date counted 2	`[2027, 8, 6]`	`[2027, 8, 9]`	Failed
partial repair probe 1	`[2027, 10, 1]`	`[2027, 10, 4]`	Failed
partial repair probe 2	`[2021, 1, 20]`	`[2021, 1, 21]`	Failed
boundary control 1	`[2024, 5, 3]`	`[2024, 5, 3]`	Passed
normal control 1	`[2029, 3, 5]`	`[2029, 3, 5]`	Passed
normal control 2	`[2020, 6, 30]`	`[2020, 6, 30]`	Passed
normal control 3	`[2022, 7, 21]`	`[2022, 7, 21]`	Passed

SHA-256 / 89bc1e1e389568aa935255f34867287f1a388b644778e298b693c41314d88c88

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import datetime
N = 1
observations = []
def solve(trade, n, hol_a, hol_b):
    T = datetime.date(*trade)
    HA = {datetime.date(*h) for h in hol_a}
    HB = {datetime.date(*h) for h in hol_b}
    def biz(x):
        return x.weekday() < 5 and x not in HA and x not in HB
    x = T
    k = 0
    while k < n:
        if biz(x) and x != T:
            k += 1
        x += datetime.timedelta(days=1)
    return [x.year, x.month, x.day]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression trade date counted 1', [[2028, 3, 31], 5, [[2028, 4, 3], [2028, 4, 6]], [[2028, 4, 4], [2028, 4, 7]]], [2028, 4, 13]], ['regression trade date counted 2', [[2027, 8, 5], 2, [], [[2027, 8, 7]]], [2027, 8, 9]], ['partial repair probe 1', [[2027, 9, 30], 2, [], [[2027, 10, 3]]], [2027, 10, 4]], ['partial repair probe 2', [[2021, 1, 18], 2, [[2021, 1, 27]], [[2021, 1, 27], [2021, 1, 19]]], [2021, 1, 21]], ['boundary control 1', [[2024, 5, 3], 0, [], []], [2024, 5, 3]], ['normal control 1', [[2029, 3, 5], 0, [], [[2029, 3, 8], [2029, 3, 13]]], [2029, 3, 5]], ['normal control 2', [[2020, 6, 30], 0, [], []], [2020, 6, 30]], ['normal control 3', [[2022, 7, 21], 0, [[2022, 7, 30], [2022, 7, 25]], []], [2022, 7, 21]]], [['regression trade date counted 1', [[2030, 2, 28], 2, [], [[2030, 3, 4], [2030, 3, 1]]], [2030, 3, 6]], ['regression trade date counted 2', [[2027, 2, 5], 1, [[2027, 2, 10]], [[2027, 2, 13], [2027, 2, 8]]], [2027, 2, 9]], ['partial repair probe 1', [[2019, 5, 31], 3, [[2019, 6, 8]], []], [2019, 6, 5]], ['partial repair probe 2', [[2024, 7, 31], 1, [], [[2024, 8, 9], [2024, 8, 4]]], [2024, 8, 1]], ['boundary control 1', [[2024, 5, 3], 0, [], []], [2024, 5, 3]], ['normal control 1', [[2020, 2, 28], 0, [[2020, 3, 1]], []], [2020, 2, 28]], ['normal control 2', [[2024, 4, 22], 0, [], []], [2024, 4, 22]], ['normal control 3', [[2021, 1, 25], 0, [[2021, 2, 3], [2021, 2, 1]], [[2021, 1, 29], [2021, 1, 30]]], [2021, 1, 25]]], [['regression trade date counted 1', [[2027, 7, 21], 2, [[2027, 7, 23], [2027, 7, 30]], [[2027, 7, 28], [2027, 7, 26]]], [2027, 7, 27]], ['regression trade date counted 2', [[2026, 6, 30], 1, [[2026, 7, 1], [2026, 7, 6]], [[2026, 7, 2], [2026, 7, 5]]], [2026, 7, 3]], ['partial repair probe 1', [[2021, 10, 15], 3, [], [[2021, 10, 24]]], [2021, 10, 20]], ['partial repair probe 2', [[2025, 10, 31], 2, [[2025, 11, 1]], [[2025, 11, 9]]], [2025, 11, 4]], ['boundary control 1', [[2024, 5, 3], 0, [], []], [2024, 5, 3]], ['normal control 1', [[2022, 1, 21], 0, [[2022, 1, 23], [2022, 1, 22]], [[2022, 1, 26], [2022, 1, 29]]], [2022, 1, 21]], ['normal control 2', [[2025, 9, 22], 0, [[2025, 9, 26]], [[2025, 9, 27], [2025, 9, 26]]], [2025, 9, 22]], ['normal control 3', [[2023, 2, 28], 0, [[2023, 3, 8]], [[2023, 3, 4]]], [2023, 2, 28]]], [['regression trade date counted 1', [[2019, 7, 31], 2, [[2019, 8, 2]], []], [2019, 8, 5]], ['regression trade date counted 2', [[2026, 1, 5], 2, [], [[2026, 1, 11]]], [2026, 1, 7]], ['partial repair probe 1', [[2030, 5, 31], 3, [[2030, 6, 2]], []], [2030, 6, 5]], ['partial repair probe 2', [[2023, 10, 31], 2, [[2023, 11, 7], [2023, 11, 2]], [[2023, 11, 3], [2023, 11, 2]]], [2023, 11, 6]], ['boundary control 1', [[2024, 5, 3], 0, [], []], [2024, 5, 3]], ['normal control 1', [[2020, 4, 30], 0, [[2020, 5, 7]], [[2020, 5, 5], [2020, 5, 1]]], [2020, 4, 30]], ['normal control 2', [[2019, 8, 6], 0, [[2019, 8, 12]], []], [2019, 8, 6]], ['normal control 3', [[2019, 7, 31], 0, [], []], [2019, 7, 31]]], [['regression trade date counted 1', [[2026, 12, 31], 2, [], []], [2027, 1, 4]], ['regression trade date counted 2', [[2026, 11, 9], 2, [[2026, 11, 16]], [[2026, 11, 18], [2026, 11, 12]]], [2026, 11, 11]], ['partial repair probe 1', [[2019, 7, 1], 5, [], []], [2019, 7, 8]], ['partial repair probe 2', [[2029, 5, 28], 2, [], [[2029, 6, 1]]], [2029, 5, 30]], ['boundary control 1', [[2024, 5, 3], 0, [], []], [2024, 5, 3]], ['normal control 1', [[2025, 6, 2], 0, [[2025, 6, 8]], [[2025, 6, 5], [2025, 6, 9]]], [2025, 6, 2]], ['normal control 2', [[2021, 9, 10], 0, [], [[2021, 9, 19]]], [2021, 9, 10]], ['normal control 3', [[2020, 10, 26], 0, [[2020, 10, 28], [2020, 10, 31]], [[2020, 11, 3], [2020, 11, 4]]], [2020, 10, 26]]]]
for label, args, expected in fixtures[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 trade date counted 1	`[2028, 4, 14]`	`[2028, 4, 13]`	Failed
regression trade date counted 2	`[2027, 8, 10]`	`[2027, 8, 9]`	Failed
partial repair probe 1	`[2027, 10, 5]`	`[2027, 10, 4]`	Failed
partial repair probe 2	`[2021, 1, 22]`	`[2021, 1, 21]`	Failed
boundary control 1	`[2024, 5, 3]`	`[2024, 5, 3]`	Passed
normal control 1	`[2029, 3, 5]`	`[2029, 3, 5]`	Passed
normal control 2	`[2020, 6, 30]`	`[2020, 6, 30]`	Passed
normal control 3	`[2022, 7, 21]`	`[2022, 7, 21]`	Passed

SHA-256 / 89d8b6dbf6349fbceb17a8a577d38af7be419390edfc220912865990a9e5b65e

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
import datetime
N = 1
observations = []
def solve(trade, n, hol_a, hol_b):
    T = datetime.date(*trade)
    HA = {datetime.date(*h) for h in hol_a}
    HB = {datetime.date(*h) for h in hol_b}
    def biz(x):
        return x.weekday() < 5 and x not in HA and x not in HB
    x = T
    k = 0
    while k < n:
        x += datetime.timedelta(days=1)
        if biz(x):
            k += 1
    return [x.year, x.month, x.day]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression trade date counted 1', [[2028, 3, 31], 5, [[2028, 4, 3], [2028, 4, 6]], [[2028, 4, 4], [2028, 4, 7]]], [2028, 4, 13]], ['regression trade date counted 2', [[2027, 8, 5], 2, [], [[2027, 8, 7]]], [2027, 8, 9]], ['partial repair probe 1', [[2027, 9, 30], 2, [], [[2027, 10, 3]]], [2027, 10, 4]], ['partial repair probe 2', [[2021, 1, 18], 2, [[2021, 1, 27]], [[2021, 1, 27], [2021, 1, 19]]], [2021, 1, 21]], ['boundary control 1', [[2024, 5, 3], 0, [], []], [2024, 5, 3]], ['normal control 1', [[2029, 3, 5], 0, [], [[2029, 3, 8], [2029, 3, 13]]], [2029, 3, 5]], ['normal control 2', [[2020, 6, 30], 0, [], []], [2020, 6, 30]], ['normal control 3', [[2022, 7, 21], 0, [[2022, 7, 30], [2022, 7, 25]], []], [2022, 7, 21]]], [['regression trade date counted 1', [[2030, 2, 28], 2, [], [[2030, 3, 4], [2030, 3, 1]]], [2030, 3, 6]], ['regression trade date counted 2', [[2027, 2, 5], 1, [[2027, 2, 10]], [[2027, 2, 13], [2027, 2, 8]]], [2027, 2, 9]], ['partial repair probe 1', [[2019, 5, 31], 3, [[2019, 6, 8]], []], [2019, 6, 5]], ['partial repair probe 2', [[2024, 7, 31], 1, [], [[2024, 8, 9], [2024, 8, 4]]], [2024, 8, 1]], ['boundary control 1', [[2024, 5, 3], 0, [], []], [2024, 5, 3]], ['normal control 1', [[2020, 2, 28], 0, [[2020, 3, 1]], []], [2020, 2, 28]], ['normal control 2', [[2024, 4, 22], 0, [], []], [2024, 4, 22]], ['normal control 3', [[2021, 1, 25], 0, [[2021, 2, 3], [2021, 2, 1]], [[2021, 1, 29], [2021, 1, 30]]], [2021, 1, 25]]], [['regression trade date counted 1', [[2027, 7, 21], 2, [[2027, 7, 23], [2027, 7, 30]], [[2027, 7, 28], [2027, 7, 26]]], [2027, 7, 27]], ['regression trade date counted 2', [[2026, 6, 30], 1, [[2026, 7, 1], [2026, 7, 6]], [[2026, 7, 2], [2026, 7, 5]]], [2026, 7, 3]], ['partial repair probe 1', [[2021, 10, 15], 3, [], [[2021, 10, 24]]], [2021, 10, 20]], ['partial repair probe 2', [[2025, 10, 31], 2, [[2025, 11, 1]], [[2025, 11, 9]]], [2025, 11, 4]], ['boundary control 1', [[2024, 5, 3], 0, [], []], [2024, 5, 3]], ['normal control 1', [[2022, 1, 21], 0, [[2022, 1, 23], [2022, 1, 22]], [[2022, 1, 26], [2022, 1, 29]]], [2022, 1, 21]], ['normal control 2', [[2025, 9, 22], 0, [[2025, 9, 26]], [[2025, 9, 27], [2025, 9, 26]]], [2025, 9, 22]], ['normal control 3', [[2023, 2, 28], 0, [[2023, 3, 8]], [[2023, 3, 4]]], [2023, 2, 28]]], [['regression trade date counted 1', [[2019, 7, 31], 2, [[2019, 8, 2]], []], [2019, 8, 5]], ['regression trade date counted 2', [[2026, 1, 5], 2, [], [[2026, 1, 11]]], [2026, 1, 7]], ['partial repair probe 1', [[2030, 5, 31], 3, [[2030, 6, 2]], []], [2030, 6, 5]], ['partial repair probe 2', [[2023, 10, 31], 2, [[2023, 11, 7], [2023, 11, 2]], [[2023, 11, 3], [2023, 11, 2]]], [2023, 11, 6]], ['boundary control 1', [[2024, 5, 3], 0, [], []], [2024, 5, 3]], ['normal control 1', [[2020, 4, 30], 0, [[2020, 5, 7]], [[2020, 5, 5], [2020, 5, 1]]], [2020, 4, 30]], ['normal control 2', [[2019, 8, 6], 0, [[2019, 8, 12]], []], [2019, 8, 6]], ['normal control 3', [[2019, 7, 31], 0, [], []], [2019, 7, 31]]], [['regression trade date counted 1', [[2026, 12, 31], 2, [], []], [2027, 1, 4]], ['regression trade date counted 2', [[2026, 11, 9], 2, [[2026, 11, 16]], [[2026, 11, 18], [2026, 11, 12]]], [2026, 11, 11]], ['partial repair probe 1', [[2019, 7, 1], 5, [], []], [2019, 7, 8]], ['partial repair probe 2', [[2029, 5, 28], 2, [], [[2029, 6, 1]]], [2029, 5, 30]], ['boundary control 1', [[2024, 5, 3], 0, [], []], [2024, 5, 3]], ['normal control 1', [[2025, 6, 2], 0, [[2025, 6, 8]], [[2025, 6, 5], [2025, 6, 9]]], [2025, 6, 2]], ['normal control 2', [[2021, 9, 10], 0, [], [[2021, 9, 19]]], [2021, 9, 10]], ['normal control 3', [[2020, 10, 26], 0, [[2020, 10, 28], [2020, 10, 31]], [[2020, 11, 3], [2020, 11, 4]]], [2020, 10, 26]]]]
for label, args, expected in fixtures[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 trade date counted 1	`[2028, 4, 13]`	`[2028, 4, 13]`	Passed
regression trade date counted 2	`[2027, 8, 9]`	`[2027, 8, 9]`	Passed
partial repair probe 1	`[2027, 10, 4]`	`[2027, 10, 4]`	Passed
partial repair probe 2	`[2021, 1, 21]`	`[2021, 1, 21]`	Passed
boundary control 1	`[2024, 5, 3]`	`[2024, 5, 3]`	Passed
normal control 1	`[2029, 3, 5]`	`[2029, 3, 5]`	Passed
normal control 2	`[2020, 6, 30]`	`[2020, 6, 30]`	Passed
normal control 3	`[2022, 7, 21]`	`[2022, 7, 21]`	Passed

SHA-256 / af529db1972c854a87db36c6615485af0d5b8eb45404c03a05f9787769aace1c

Verification & scope

A deterministic toy contract stated explicitly in the contract field; no claim of conformance to any published convention text. 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 2026-09-29T14:46:53.102294+00:00.

Case digest / 143c11e012c49c23906abff3bc7f07fe07b92228001f9cae5204fdcdf66a0244