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FA-83476 / Card game rule engines / Open access

Equal deadwood is not an undercut · case 01

A defender matching the knocker deadwood loses instead of undercutting.

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

ROOT CAUSE

The undercut test uses strict less-than.

VERIFIED REPAIR

Defender deadwood <= knocker deadwood is an undercut.

Unsuccessful approach: Awarding a flat 25 drops the deadwood difference from the undercut.

Case contract

Input [knocker_deadwood_cards, defender_deadwood_after_layoffs, gin, big_gin]. Deadwood: A=1, T/J/Q/K=10, others pip. Knocking above 10 is ["illegal", 0]. Big gin scores 31 + defender deadwood, gin 25 + defender deadwood (gin cannot be undercut). Otherwise if defender deadwood <= knocker deadwood the defender undercuts for 25 + difference; else knocker scores the difference.

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):
    kc, dc, gin, big = x
    def dw(cards):
        t = 0
        for c in cards:
            r = c[0]
            t += 1 if r == 'A' else 10 if r in 'TJQK' else int(r)
        return t
    k = dw(kc)
    d = dw(dc)
    if k > 10:
        return ['illegal', 0]
    if big:
        return ['knocker', 31 + d]
    if gin:
        return ['knocker', 25 + d]
    if d < k:
        return ['defender', 25 + k - d]
    return ['knocker', d - k]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[[[], [], False, False], ['defender', 25]], [[[], ['KS', '5S', '4H'], False, False], ['knocker', 19]], [[['KD', 'JH', '9S'], ['JS', '7D'], False, False], ['illegal', 0]], [[['4S', '4D', 'AS'], ['3D', 'JS', 'KD', '7D'], False, False], ['knocker', 21]], [[['TS', 'JC', '5S'], ['4H', '7C'], False, False], ['illegal', 0]], [[[], ['KS', 'TD', '5D', '7D'], False, False], ['knocker', 32]], [[[], ['7H', '5D'], False, False], ['knocker', 12]], [[['KS'], [], False, False], ['defender', 35]]], [[[['6S', '8S', '6C'], ['4C', 'KH', '9S'], False, False], ['illegal', 0]], [[[], [], True, False], ['knocker', 25]], [[['6C'], [], False, False], ['defender', 31]], [[[], ['4D', 'JS'], True, False], ['knocker', 39]], [[['4S'], ['JH', '9H', '8C'], False, False], ['knocker', 23]], [[[], ['KH', '3D'], False, False], ['knocker', 13]], [[[], [], False, False], ['defender', 25]], [[['2H'], [], False, False], ['defender', 27]]], [[[['KH', '4H', 'JD'], [], False, False], ['illegal', 0]], [[[], ['8S', 'QD'], True, False], ['knocker', 43]], [[['7D', '7S'], ['2S', 'QC'], False, False], ['illegal', 0]], [[['2C'], ['2D', 'AH', 'JD', '5S'], False, False], ['knocker', 16]], [[[], ['3C', '3H', '5S'], True, False], ['knocker', 36]], [[['AC', '9D', 'AD'], ['8S'], False, False], ['illegal', 0]], [[['JC'], ['AC', 'AH'], False, False], ['defender', 33]], [[[], [], False, False], ['defender', 25]]], [[[[], ['JS', '8H', '7C'], False, False], ['knocker', 25]], [[[], ['2C'], False, False], ['knocker', 2]], [[[], ['KD'], False, False], ['knocker', 10]], [[[], [], True, False], ['knocker', 25]], [[['TH', '3H', 'KC'], ['TD', 'AS', 'JD', '5H'], False, False], ['illegal', 0]], [[['TH', '8S'], ['QC', '5S', '2S', '6D'], False, False], ['illegal', 0]], [[['QD'], [], False, False], ['defender', 35]], [[['3S'], ['2C', 'AD'], False, False], ['defender', 25]]], [[[[], [], False, False], ['defender', 25]], [[['TH', '6C'], ['6D', 'QC'], False, False], ['illegal', 0]], [[['9C'], ['8S', 'JD'], False, False], ['knocker', 9]], [[['5H', '6D'], ['QH', '8D', 'KH'], False, False], ['illegal', 0]], [[['QC', 'JD'], ['7C', 'KH', '8C', '5S'], False, False], ['illegal', 0]], [[[], ['4D', '3S'], False, False], ['knocker', 7]], [[['8D', 'AH'], [], False, False], ['defender', 34]], [[['6D', '6H'], ['6C', 'QD', '9S', '5C'], False, False], ['illegal', 0]]]]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("knock score 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
knock score case 0['knocker', 0]['defender', 25]Failed
knock score case 1['knocker', 19]['knocker', 19]Passed
knock score case 2['illegal', 0]['illegal', 0]Passed
knock score case 3['knocker', 21]['knocker', 21]Passed
knock score case 4['illegal', 0]['illegal', 0]Passed
knock score case 5['knocker', 32]['knocker', 32]Passed
knock score case 6['knocker', 12]['knocker', 12]Passed
knock score case 7['defender', 35]['defender', 35]Passed

SHA-256 / 36a36130ece0a84b7863722dede6702af521e8e482f9b2d220925a567d1dda84

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(x):
    kc, dc, gin, big = x
    def dw(cards):
        t = 0
        for c in cards:
            r = c[0]
            t += 1 if r == 'A' else 10 if r in 'TJQK' else int(r)
        return t
    k = dw(kc)
    d = dw(dc)
    if k > 10:
        return ['illegal', 0]
    if big:
        return ['knocker', 31 + d]
    if gin:
        return ['knocker', 25 + d]
    if d <= k:
        return ['defender', 25]
    return ['knocker', d - k]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[[[], [], False, False], ['defender', 25]], [[[], ['KS', '5S', '4H'], False, False], ['knocker', 19]], [[['KD', 'JH', '9S'], ['JS', '7D'], False, False], ['illegal', 0]], [[['4S', '4D', 'AS'], ['3D', 'JS', 'KD', '7D'], False, False], ['knocker', 21]], [[['TS', 'JC', '5S'], ['4H', '7C'], False, False], ['illegal', 0]], [[[], ['KS', 'TD', '5D', '7D'], False, False], ['knocker', 32]], [[[], ['7H', '5D'], False, False], ['knocker', 12]], [[['KS'], [], False, False], ['defender', 35]]], [[[['6S', '8S', '6C'], ['4C', 'KH', '9S'], False, False], ['illegal', 0]], [[[], [], True, False], ['knocker', 25]], [[['6C'], [], False, False], ['defender', 31]], [[[], ['4D', 'JS'], True, False], ['knocker', 39]], [[['4S'], ['JH', '9H', '8C'], False, False], ['knocker', 23]], [[[], ['KH', '3D'], False, False], ['knocker', 13]], [[[], [], False, False], ['defender', 25]], [[['2H'], [], False, False], ['defender', 27]]], [[[['KH', '4H', 'JD'], [], False, False], ['illegal', 0]], [[[], ['8S', 'QD'], True, False], ['knocker', 43]], [[['7D', '7S'], ['2S', 'QC'], False, False], ['illegal', 0]], [[['2C'], ['2D', 'AH', 'JD', '5S'], False, False], ['knocker', 16]], [[[], ['3C', '3H', '5S'], True, False], ['knocker', 36]], [[['AC', '9D', 'AD'], ['8S'], False, False], ['illegal', 0]], [[['JC'], ['AC', 'AH'], False, False], ['defender', 33]], [[[], [], False, False], ['defender', 25]]], [[[[], ['JS', '8H', '7C'], False, False], ['knocker', 25]], [[[], ['2C'], False, False], ['knocker', 2]], [[[], ['KD'], False, False], ['knocker', 10]], [[[], [], True, False], ['knocker', 25]], [[['TH', '3H', 'KC'], ['TD', 'AS', 'JD', '5H'], False, False], ['illegal', 0]], [[['TH', '8S'], ['QC', '5S', '2S', '6D'], False, False], ['illegal', 0]], [[['QD'], [], False, False], ['defender', 35]], [[['3S'], ['2C', 'AD'], False, False], ['defender', 25]]], [[[[], [], False, False], ['defender', 25]], [[['TH', '6C'], ['6D', 'QC'], False, False], ['illegal', 0]], [[['9C'], ['8S', 'JD'], False, False], ['knocker', 9]], [[['5H', '6D'], ['QH', '8D', 'KH'], False, False], ['illegal', 0]], [[['QC', 'JD'], ['7C', 'KH', '8C', '5S'], False, False], ['illegal', 0]], [[[], ['4D', '3S'], False, False], ['knocker', 7]], [[['8D', 'AH'], [], False, False], ['defender', 34]], [[['6D', '6H'], ['6C', 'QD', '9S', '5C'], False, False], ['illegal', 0]]]]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("knock score 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
knock score case 0['defender', 25]['defender', 25]Passed
knock score case 1['knocker', 19]['knocker', 19]Passed
knock score case 2['illegal', 0]['illegal', 0]Passed
knock score case 3['knocker', 21]['knocker', 21]Passed
knock score case 4['illegal', 0]['illegal', 0]Passed
knock score case 5['knocker', 32]['knocker', 32]Passed
knock score case 6['knocker', 12]['knocker', 12]Passed
knock score case 7['defender', 25]['defender', 35]Failed

SHA-256 / 300e903f9537784e596a66c28f2adfaa91c01e01bc2111860824a1ca64cc2051

3 / The verified repair

Exit 0
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    kc, dc, gin, big = x
    def dw(cards):
        t = 0
        for c in cards:
            r = c[0]
            t += 1 if r == 'A' else 10 if r in 'TJQK' else int(r)
        return t
    k = dw(kc)
    d = dw(dc)
    if k > 10:
        return ['illegal', 0]
    if big:
        return ['knocker', 31 + d]
    if gin:
        return ['knocker', 25 + d]
    if d <= k:
        return ['defender', 25 + k - d]
    return ['knocker', d - k]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[[[], [], False, False], ['defender', 25]], [[[], ['KS', '5S', '4H'], False, False], ['knocker', 19]], [[['KD', 'JH', '9S'], ['JS', '7D'], False, False], ['illegal', 0]], [[['4S', '4D', 'AS'], ['3D', 'JS', 'KD', '7D'], False, False], ['knocker', 21]], [[['TS', 'JC', '5S'], ['4H', '7C'], False, False], ['illegal', 0]], [[[], ['KS', 'TD', '5D', '7D'], False, False], ['knocker', 32]], [[[], ['7H', '5D'], False, False], ['knocker', 12]], [[['KS'], [], False, False], ['defender', 35]]], [[[['6S', '8S', '6C'], ['4C', 'KH', '9S'], False, False], ['illegal', 0]], [[[], [], True, False], ['knocker', 25]], [[['6C'], [], False, False], ['defender', 31]], [[[], ['4D', 'JS'], True, False], ['knocker', 39]], [[['4S'], ['JH', '9H', '8C'], False, False], ['knocker', 23]], [[[], ['KH', '3D'], False, False], ['knocker', 13]], [[[], [], False, False], ['defender', 25]], [[['2H'], [], False, False], ['defender', 27]]], [[[['KH', '4H', 'JD'], [], False, False], ['illegal', 0]], [[[], ['8S', 'QD'], True, False], ['knocker', 43]], [[['7D', '7S'], ['2S', 'QC'], False, False], ['illegal', 0]], [[['2C'], ['2D', 'AH', 'JD', '5S'], False, False], ['knocker', 16]], [[[], ['3C', '3H', '5S'], True, False], ['knocker', 36]], [[['AC', '9D', 'AD'], ['8S'], False, False], ['illegal', 0]], [[['JC'], ['AC', 'AH'], False, False], ['defender', 33]], [[[], [], False, False], ['defender', 25]]], [[[[], ['JS', '8H', '7C'], False, False], ['knocker', 25]], [[[], ['2C'], False, False], ['knocker', 2]], [[[], ['KD'], False, False], ['knocker', 10]], [[[], [], True, False], ['knocker', 25]], [[['TH', '3H', 'KC'], ['TD', 'AS', 'JD', '5H'], False, False], ['illegal', 0]], [[['TH', '8S'], ['QC', '5S', '2S', '6D'], False, False], ['illegal', 0]], [[['QD'], [], False, False], ['defender', 35]], [[['3S'], ['2C', 'AD'], False, False], ['defender', 25]]], [[[[], [], False, False], ['defender', 25]], [[['TH', '6C'], ['6D', 'QC'], False, False], ['illegal', 0]], [[['9C'], ['8S', 'JD'], False, False], ['knocker', 9]], [[['5H', '6D'], ['QH', '8D', 'KH'], False, False], ['illegal', 0]], [[['QC', 'JD'], ['7C', 'KH', '8C', '5S'], False, False], ['illegal', 0]], [[[], ['4D', '3S'], False, False], ['knocker', 7]], [[['8D', 'AH'], [], False, False], ['defender', 34]], [[['6D', '6H'], ['6C', 'QD', '9S', '5C'], False, False], ['illegal', 0]]]]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("knock score 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
knock score case 0['defender', 25]['defender', 25]Passed
knock score case 1['knocker', 19]['knocker', 19]Passed
knock score case 2['illegal', 0]['illegal', 0]Passed
knock score case 3['knocker', 21]['knocker', 21]Passed
knock score case 4['illegal', 0]['illegal', 0]Passed
knock score case 5['knocker', 32]['knocker', 32]Passed
knock score case 6['knocker', 12]['knocker', 12]Passed
knock score case 7['defender', 35]['defender', 35]Passed

SHA-256 / 75d452b84ba53e4b34aef33df260deeeb334e1e96d17b23faea5bfb1ab5445f0

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 2026-09-29T14:50:21.952294+00:00.

Case digest / d27e96a9a98058bc55dee10ac9a3bfb616c8967758bca63429b1c86f59875daf