FAILURE MAP
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FA-83756 / Card game rule engines / Open access

Four of a kind is accepted as a plain combination · case 01

Four same-rank cards are played like a triple.

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

ROOT CAUSE

The size cap on same-rank plays is missing.

THE FAILURE

The size cap on same-rank plays is missing.

Unsuccessful approach: Capping at four still admits four of a kind.

Case contract

Input [current_combination, play]. Ranks 3 low to 2 high; suits D<C<H<S. A play is 1-3 cards of one rank. On an empty table any valid play is "ok"; otherwise it must have the same size and its highest card must outrank the current highest card (rank, then suit). Empty play is "pass". Return "ok", "invalid" or "pass".

Why this case matters

Card-game engines, scoring apps and online tables apply this rule automatically on every hand.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    cur, play = x
    order = '3456789TJQKA2'
    suits = 'DCHS'
    def key(c):
        return (order.index(c[0]), suits.index(c[1]))
    if not play:
        return 'pass'
    if len(set(c[0] for c in play)) != 1:
        return 'invalid'
    if not cur:
        return 'ok'
    if len(play) != len(cur):
        return 'invalid'
    if max(key(c) for c in play) > max(key(c) for c in cur):
        return 'ok'
    return 'invalid'
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[[[], ['KD']], 'ok'], [[['KC', 'KD'], ['KH', 'KS']], 'ok'], [[['8S', '8C', '8H'], ['KD', 'KC', 'KS']], 'ok'], [[['6S'], ['6H']], 'invalid'], [[['9C'], ['6S']], 'invalid'], [[[], ['3H', '3S', '3C']], 'ok'], [[[], ['KD', 'KS', 'KH', 'KC']], 'invalid'], [[[], ['KD', 'KS', 'KH', 'KC']], 'invalid']], [[[['8D', '8H'], ['8S', '8D', '8H', '8C']], 'invalid'], [[['AS'], ['AH', 'AC', 'AD']], 'invalid'], [[[], ['3C']], 'ok'], [[['QD'], ['QH']], 'ok'], [[['JD', 'JS'], ['TD', 'TS', 'TC', 'TH']], 'invalid'], [[['9S', '9H'], ['8S', '8C']], 'invalid'], [[[], ['KD', 'KS', 'KH', 'KC']], 'invalid'], [[[], ['4S', '4H', '4D', '4C']], 'invalid']], [[[['9D', '9C'], ['9D', '9C']], 'invalid'], [[['KD'], ['AH']], 'ok'], [[[], ['KS', 'KD']], 'ok'], [[['JC'], ['7C']], 'invalid'], [[['5S'], ['5H']], 'invalid'], [[['2S'], ['5D']], 'invalid'], [[[], ['KD', 'KS', 'KH', 'KC']], 'invalid'], [[[], ['4S', '4D', '4H', '4C']], 'invalid']], [[[['JH', 'JC'], ['JC', 'JS']], 'ok'], [[['7C'], ['2D']], 'ok'], [[['2H'], ['2H']], 'invalid'], [[['TH', 'TD'], ['8D', '2S']], 'invalid'], [[['5H', '5D'], ['JS', 'JC']], 'ok'], [[[], ['QC', 'QH']], 'ok'], [[[], ['KD', 'KS', 'KH', 'KC']], 'invalid'], [[[], ['KD', 'KS', 'KH', 'KC']], 'invalid']], [[[['6C', '6H'], ['AH', '4D']], 'invalid'], [[['3D', '3H', '3C'], ['3S', '3D', '3H', 'AC']], 'invalid'], [[['5S'], ['3S']], 'invalid'], [[['9C'], ['9C']], 'invalid'], [[['7C', '7S', '7D'], ['3D', '3S', '3C']], 'invalid'], [[['3H', '3C'], ['3D', '3C', '3S', '3H']], 'invalid'], [[[], ['KD', 'KS', 'KH', 'KC']], 'invalid'], [[[], ['4S', '4H', '4D', '4C']], 'invalid']]]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("play case %d" % i, 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 fixtureActualExpectedOutcome
play case 0okokPassed
play case 1okokPassed
play case 2okokPassed
play case 3invalidinvalidPassed
play case 4invalidinvalidPassed
play case 5okokPassed
play case 6okinvalidFailed
play case 7okinvalidFailed

SHA-256 / 9b1482bf23acd1eb06f9df98be4a01b1cedc254d51af0f3ebce14106d2e67cfc

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    cur, play = x
    order = '3456789TJQKA2'
    suits = 'DCHS'
    def key(c):
        return (order.index(c[0]), suits.index(c[1]))
    if not play:
        return 'pass'
    if len(set(c[0] for c in play)) != 1 or len(play) > 4:
        return 'invalid'
    if not cur:
        return 'ok'
    if len(play) != len(cur):
        return 'invalid'
    if max(key(c) for c in play) > max(key(c) for c in cur):
        return 'ok'
    return 'invalid'
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[[[], ['KD']], 'ok'], [[['KC', 'KD'], ['KH', 'KS']], 'ok'], [[['8S', '8C', '8H'], ['KD', 'KC', 'KS']], 'ok'], [[['6S'], ['6H']], 'invalid'], [[['9C'], ['6S']], 'invalid'], [[[], ['3H', '3S', '3C']], 'ok'], [[[], ['KD', 'KS', 'KH', 'KC']], 'invalid'], [[[], ['KD', 'KS', 'KH', 'KC']], 'invalid']], [[[['8D', '8H'], ['8S', '8D', '8H', '8C']], 'invalid'], [[['AS'], ['AH', 'AC', 'AD']], 'invalid'], [[[], ['3C']], 'ok'], [[['QD'], ['QH']], 'ok'], [[['JD', 'JS'], ['TD', 'TS', 'TC', 'TH']], 'invalid'], [[['9S', '9H'], ['8S', '8C']], 'invalid'], [[[], ['KD', 'KS', 'KH', 'KC']], 'invalid'], [[[], ['4S', '4H', '4D', '4C']], 'invalid']], [[[['9D', '9C'], ['9D', '9C']], 'invalid'], [[['KD'], ['AH']], 'ok'], [[[], ['KS', 'KD']], 'ok'], [[['JC'], ['7C']], 'invalid'], [[['5S'], ['5H']], 'invalid'], [[['2S'], ['5D']], 'invalid'], [[[], ['KD', 'KS', 'KH', 'KC']], 'invalid'], [[[], ['4S', '4D', '4H', '4C']], 'invalid']], [[[['JH', 'JC'], ['JC', 'JS']], 'ok'], [[['7C'], ['2D']], 'ok'], [[['2H'], ['2H']], 'invalid'], [[['TH', 'TD'], ['8D', '2S']], 'invalid'], [[['5H', '5D'], ['JS', 'JC']], 'ok'], [[[], ['QC', 'QH']], 'ok'], [[[], ['KD', 'KS', 'KH', 'KC']], 'invalid'], [[[], ['KD', 'KS', 'KH', 'KC']], 'invalid']], [[[['6C', '6H'], ['AH', '4D']], 'invalid'], [[['3D', '3H', '3C'], ['3S', '3D', '3H', 'AC']], 'invalid'], [[['5S'], ['3S']], 'invalid'], [[['9C'], ['9C']], 'invalid'], [[['7C', '7S', '7D'], ['3D', '3S', '3C']], 'invalid'], [[['3H', '3C'], ['3D', '3C', '3S', '3H']], 'invalid'], [[[], ['KD', 'KS', 'KH', 'KC']], 'invalid'], [[[], ['4S', '4H', '4D', '4C']], 'invalid']]]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("play case %d" % i, 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 fixtureActualExpectedOutcome
play case 0okokPassed
play case 1okokPassed
play case 2okokPassed
play case 3invalidinvalidPassed
play case 4invalidinvalidPassed
play case 5okokPassed
play case 6okinvalidFailed
play case 7okinvalidFailed

SHA-256 / 29992ec5dcadfa582d8450c27505fd79d23af1655bf4a56323e518d48e35616a

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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Verification & scope

A bounded toy rule contract stated explicitly in the contract field; cards are two-character codes (rank, suit). Not a complete implementation of any published rulebook or casino table 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 2026-09-29T14:50:24.579020+00:00.

Case digest / 31b53b9300da2d7bcb52a9dc9356afedd8967728353c48e7a91ce67d51f5172b