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FA-67116 / Railway interlocking logic / Open access

Two-out-of-three occupancy voting: discrepancy reset · case 01

A channel is isolated after scattered, non-consecutive discrepancies.

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

ROOT CAUSE

The discrepancy count is never reset when the channel agrees.

VERIFIED REPAIR

Reset the count whenever the channel agrees or reports failure.

Unsuccessful approach: Not resetting on a failed report lets discrepancies straddle a failure.

Case contract

Three channels report occupancy (True/False) or None when failed. A channel isolated earlier counts as None. With fewer than two healthy channels the vote is occupied. Otherwise the vote is occupied when occupied reports are at least as many as clear ones (ties are occupied). A healthy channel that disagrees with the vote increments its discrepancy count, otherwise (agreeing or None) the count resets; a channel is isolated for good when its count reaches isolate_after. Return all votes and isolated channel indices.

Why this case matters

Interlocking logic decides whether trains may be given authority; a wrong decision at this point either grants unsafe movements or strands traffic.

1 / The failure

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

N = 1
observations = []
def solve(x):
    k = x['isolate_after']
    bad = [0, 0, 0]
    iso = [False, False, False]
    votes = []
    for cyc in x['cycles']:
        vals = [None if iso[i] else cyc[i] for i in range(3)]
        healthy = [v for v in vals if v is not None]
        if len(healthy) < 2:
            vote = True
        else:
            t = sum(1 for v in healthy if v)
            f = len(healthy) - t
            vote = t >= f
        votes.append(vote)
        for i in range(3):
            if vals[i] is not None and vals[i] != vote:
                bad[i] += 1
                if bad[i] >= k:
                    iso[i] = True
            else:
                pass
    return {'votes': votes, 'isolated': [i for i in range(3) if iso[i]]}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression: dissent interrupted by failure', {'isolate_after': 2, 'cycles': [[True, False, False], [None, False, False], [True, False, False]]}, {'votes': [False, False, False], 'isolated': []}), ('sampled regression 10', {'isolate_after': 2, 'cycles': [[None, True, False], [False, None, True], [False, False, False], [False, True, False], [False, True, False], [True, True, False], [False, None, False], [True, True, True]]}, {'votes': [True, True, False, False, False, True, False, True], 'isolated': [1]}), ('sampled regression 9', {'isolate_after': 3, 'cycles': [[None, False, False], [None, True, False], [False, None, None], [False, False, True], [True, None, False], [True, True, True], [None, False, None], [False, False, False], [True, None, False]]}, {'votes': [False, True, True, False, True, True, True, False, True], 'isolated': []}), ('boundary: two healthy channels disagree', {'isolate_after': 3, 'cycles': [[True, False, None]]}, {'votes': [True], 'isolated': []}), ('boundary: two healthy channels agree clear', {'isolate_after': 3, 'cycles': [[False, False, None]]}, {'votes': [False], 'isolated': []}), ('control 1', {'isolate_after': 2, 'cycles': [[False, False, False], [True, None, True], [True, True, True], [None, False, False]]}, {'votes': [False, True, True, False], 'isolated': []}), ('control 4', {'isolate_after': 2, 'cycles': [[False, True, True], [False, False, False], [False, False, False], [True, True, False], [True, True, True], [True, False, True], [False, False, False], [False, False, None], [True, True, True]]}, {'votes': [True, False, False, True, True, True, False, False, True], 'isolated': []}), ('control 7', {'isolate_after': 3, 'cycles': [[False, False, True], [False, False, False], [True, True, True], [False, True, True], [True, True, None], [False, False, False], [True, True, True], [False, False, False]]}, {'votes': [False, False, True, True, True, False, True, False], 'isolated': []})], [('regression: dissent interrupted by failure', {'isolate_after': 2, 'cycles': [[True, False, False], [None, False, False], [True, False, False]]}, {'votes': [False, False, False], 'isolated': []}), ('sampled regression 36', {'isolate_after': 3, 'cycles': [[None, True, False], [None, False, False], [False, False, True], [False, False, False], [True, True, False], [True, True, True], [True, True, None], [True, True, True]]}, {'votes': [True, False, False, False, True, True, True, True], 'isolated': []}), ('sampled regression 19', {'isolate_after': 2, 'cycles': [[True, True, True], [True, False, None], [True, False, True], [None, False, False], [True, True, None], [True, False, False], [False, False, True], [True, True, True]]}, {'votes': [True, True, True, True, True, True, True, True], 'isolated': [1]}), ('boundary: single healthy channel says clear', {'isolate_after': 3, 'cycles': [[False, None, None]]}, {'votes': [True], 'isolated': []}), ('boundary: persistent dissenter', {'isolate_after': 2, 'cycles': [[True, False, False], [True, False, False], [False, False, False]]}, {'votes': [False, False, False], 'isolated': [0]}), ('control 12', {'isolate_after': 3, 'cycles': [[False, False, False], [False, True, False], [True, False, True], [True, False, True], [False, False, True], [False, False, False], [True, False, True], [True, True, True]]}, {'votes': [False, False, True, True, True, False, True, True], 'isolated': [1]}), ('control 15', {'isolate_after': 3, 'cycles': [[False, False, False], [False, None, False], [True, False, False], [True, None, False]]}, {'votes': [False, False, False, True], 'isolated': []}), ('sampled regression 18', {'isolate_after': 2, 'cycles': [[False, False, False], [None, False, True], [False, False, True], [True, False, False], [True, False, True], [False, False, False], [False, True, None], [False, False, False], [False, False, False]]}, {'votes': [False, True, False, False, True, False, True, False, False], 'isolated': []})], [('regression: dissent interrupted by failure', {'isolate_after': 2, 'cycles': [[True, False, False], [None, False, False], [True, False, False]]}, {'votes': [False, False, False], 'isolated': []}), ('sampled regression 71', {'isolate_after': 2, 'cycles': [[False, False, None], [True, False, True], [False, False, False], [False, True, False]]}, {'votes': [False, True, False, False], 'isolated': []}), ('sampled regression 20', {'isolate_after': 2, 'cycles': [[False, True, False], [True, False, False], [True, False, None], [False, None, False], [False, True, False], [False, None, None]]}, {'votes': [False, False, True, False, False, True], 'isolated': []}), ('boundary: two dissenters in turn', {'isolate_after': 2, 'cycles': [[True, False, False], [True, False, False], [False, True, False], [False, True, False], [False, False, False]]}, {'votes': [False, False, True, True, True], 'isolated': [0, 2]}), ('boundary: isolated channel keeps reporting', {'isolate_after': 1, 'cycles': [[True, False, False], [True, True, False]]}, {'votes': [False, True], 'isolated': [0, 2]}), ('control 23', {'isolate_after': 2, 'cycles': [[True, False, True], [None, False, False], [False, False, False], [False, False, False], [False, False, None], [False, False, False], [True, None, True]]}, {'votes': [True, False, False, False, False, False, True], 'isolated': []}), ('control 26', {'isolate_after': 2, 'cycles': [[True, True, True], [False, False, False], [False, False, True], [False, False, None]]}, {'votes': [True, False, False, False], 'isolated': []}), ('sampled regression 29', {'isolate_after': 2, 'cycles': [[False, False, True], [False, False, False], [False, False, True], [False, True, False], [False, True, True]]}, {'votes': [False, False, False, False, True], 'isolated': []})], [('regression: dissent interrupted by failure', {'isolate_after': 2, 'cycles': [[True, False, False], [None, False, False], [True, False, False]]}, {'votes': [False, False, False], 'isolated': []}), ('sampled regression 9', {'isolate_after': 3, 'cycles': [[None, False, False], [None, True, False], [False, None, None], [False, False, True], [True, None, False], [True, True, True], [None, False, None], [False, False, False], [True, None, False]]}, {'votes': [False, True, True, False, True, True, True, False, True], 'isolated': []}), ('boundary: isolated channel keeps reporting', {'isolate_after': 1, 'cycles': [[True, False, False], [True, True, False]]}, {'votes': [False, True], 'isolated': [0, 2]}), ('boundary: two healthy channels disagree', {'isolate_after': 3, 'cycles': [[True, False, None]]}, {'votes': [True], 'isolated': []}), ('boundary: two healthy channels agree clear', {'isolate_after': 3, 'cycles': [[False, False, None]]}, {'votes': [False], 'isolated': []}), ('sampled regression 34', {'isolate_after': 2, 'cycles': [[True, True, False], [False, True, False], [True, True, True], [True, True, True], [True, False, True], [False, False, False], [True, False, True]]}, {'votes': [True, False, True, True, True, False, True], 'isolated': []}), ('control 37', {'isolate_after': 3, 'cycles': [[True, True, True], [False, False, False], [False, False, False], [False, True, False], [True, False, False], [False, False, False]]}, {'votes': [True, False, False, False, False, False], 'isolated': []}), ('control 40', {'isolate_after': 2, 'cycles': [[True, None, True], [False, False, None], [False, True, False], [False, True, False], [True, True, True], [True, None, False], [None, False, False], [True, True, True]]}, {'votes': [True, False, False, False, True, True, True, True], 'isolated': [1, 2]})], [('regression: dissent interrupted by failure', {'isolate_after': 2, 'cycles': [[True, False, False], [None, False, False], [True, False, False]]}, {'votes': [False, False, False], 'isolated': []}), ('sampled regression 34', {'isolate_after': 2, 'cycles': [[True, True, False], [False, True, False], [True, True, True], [True, True, True], [True, False, True], [False, False, False], [True, False, True]]}, {'votes': [True, False, True, True, True, False, True], 'isolated': []}), ('sampled regression 9', {'isolate_after': 3, 'cycles': [[None, False, False], [None, True, False], [False, None, None], [False, False, True], [True, None, False], [True, True, True], [None, False, None], [False, False, False], [True, None, False]]}, {'votes': [False, True, True, False, True, True, True, False, True], 'isolated': []}), ('boundary: two healthy channels agree clear', {'isolate_after': 3, 'cycles': [[False, False, None]]}, {'votes': [False], 'isolated': []}), ('boundary: single healthy channel says clear', {'isolate_after': 3, 'cycles': [[False, None, None]]}, {'votes': [True], 'isolated': []}), ('sampled regression 45', {'isolate_after': 2, 'cycles': [[True, True, True], [False, False, False], [False, False, False], [False, True, False], [None, True, False], [None, True, False], [True, False, False]]}, {'votes': [True, False, False, False, True, True, True], 'isolated': [2]}), ('sampled regression 48', {'isolate_after': 2, 'cycles': [[False, False, False], [False, False, False], [False, True, True], [True, True, None], [False, True, False], [True, True, True], [False, False, False], [False, False, False], [False, True, False]]}, {'votes': [False, False, True, True, False, True, False, False, False], 'isolated': []}), ('control 51', {'isolate_after': 3, 'cycles': [[False, False, False], [True, False, False], [True, True, True], [True, True, True], [True, True, True], [True, True, True], [True, False, True], [True, False, False], [True, True, True]]}, {'votes': [False, False, True, True, True, True, True, False, True], 'isolated': []})]]
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 fixtureActualExpectedOutcome
regression: dissent interrupted by failure{'isolated': [0], 'votes': [False, False, False]}{'isolated': [], 'votes': [False, False, False]}Failed
sampled regression 10{'isolated': [0, 1, 2], 'votes': [True, True, False, False, False, True, True, True]}{'isolated': [1], 'votes': [True, True, False, False, False, True, False, True]}Failed
sampled regression 9{'isolated': [2], 'votes': [False, True, True, False, True, True, True, False, True]}{'isolated': [], 'votes': [False, True, True, False, True, True, True, False, True]}Failed
boundary: two healthy channels disagree{'isolated': [], 'votes': [True]}{'isolated': [], 'votes': [True]}Passed
boundary: two healthy channels agree clear{'isolated': [], 'votes': [False]}{'isolated': [], 'votes': [False]}Passed
control 1{'isolated': [], 'votes': [False, True, True, False]}{'isolated': [], 'votes': [False, True, True, False]}Passed
control 4{'isolated': [], 'votes': [True, False, False, True, True, True, False, False, True]}{'isolated': [], 'votes': [True, False, False, True, True, True, False, False, True]}Passed
control 7{'isolated': [], 'votes': [False, False, True, True, True, False, True, False]}{'isolated': [], 'votes': [False, False, True, True, True, False, True, False]}Passed

SHA-256 / cb451719b48c35c6b3cc2718330fa38daf5698fad896cdcced1b9727aa4210c8

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(x):
    k = x['isolate_after']
    bad = [0, 0, 0]
    iso = [False, False, False]
    votes = []
    for cyc in x['cycles']:
        vals = [None if iso[i] else cyc[i] for i in range(3)]
        healthy = [v for v in vals if v is not None]
        if len(healthy) < 2:
            vote = True
        else:
            t = sum(1 for v in healthy if v)
            f = len(healthy) - t
            vote = t >= f
        votes.append(vote)
        for i in range(3):
            if vals[i] is not None and vals[i] != vote:
                bad[i] += 1
                if bad[i] >= k:
                    iso[i] = True
            elif vals[i] is not None:
                bad[i] = 0
    return {'votes': votes, 'isolated': [i for i in range(3) if iso[i]]}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression: dissent interrupted by failure', {'isolate_after': 2, 'cycles': [[True, False, False], [None, False, False], [True, False, False]]}, {'votes': [False, False, False], 'isolated': []}), ('sampled regression 10', {'isolate_after': 2, 'cycles': [[None, True, False], [False, None, True], [False, False, False], [False, True, False], [False, True, False], [True, True, False], [False, None, False], [True, True, True]]}, {'votes': [True, True, False, False, False, True, False, True], 'isolated': [1]}), ('sampled regression 9', {'isolate_after': 3, 'cycles': [[None, False, False], [None, True, False], [False, None, None], [False, False, True], [True, None, False], [True, True, True], [None, False, None], [False, False, False], [True, None, False]]}, {'votes': [False, True, True, False, True, True, True, False, True], 'isolated': []}), ('boundary: two healthy channels disagree', {'isolate_after': 3, 'cycles': [[True, False, None]]}, {'votes': [True], 'isolated': []}), ('boundary: two healthy channels agree clear', {'isolate_after': 3, 'cycles': [[False, False, None]]}, {'votes': [False], 'isolated': []}), ('control 1', {'isolate_after': 2, 'cycles': [[False, False, False], [True, None, True], [True, True, True], [None, False, False]]}, {'votes': [False, True, True, False], 'isolated': []}), ('control 4', {'isolate_after': 2, 'cycles': [[False, True, True], [False, False, False], [False, False, False], [True, True, False], [True, True, True], [True, False, True], [False, False, False], [False, False, None], [True, True, True]]}, {'votes': [True, False, False, True, True, True, False, False, True], 'isolated': []}), ('control 7', {'isolate_after': 3, 'cycles': [[False, False, True], [False, False, False], [True, True, True], [False, True, True], [True, True, None], [False, False, False], [True, True, True], [False, False, False]]}, {'votes': [False, False, True, True, True, False, True, False], 'isolated': []})], [('regression: dissent interrupted by failure', {'isolate_after': 2, 'cycles': [[True, False, False], [None, False, False], [True, False, False]]}, {'votes': [False, False, False], 'isolated': []}), ('sampled regression 36', {'isolate_after': 3, 'cycles': [[None, True, False], [None, False, False], [False, False, True], [False, False, False], [True, True, False], [True, True, True], [True, True, None], [True, True, True]]}, {'votes': [True, False, False, False, True, True, True, True], 'isolated': []}), ('sampled regression 19', {'isolate_after': 2, 'cycles': [[True, True, True], [True, False, None], [True, False, True], [None, False, False], [True, True, None], [True, False, False], [False, False, True], [True, True, True]]}, {'votes': [True, True, True, True, True, True, True, True], 'isolated': [1]}), ('boundary: single healthy channel says clear', {'isolate_after': 3, 'cycles': [[False, None, None]]}, {'votes': [True], 'isolated': []}), ('boundary: persistent dissenter', {'isolate_after': 2, 'cycles': [[True, False, False], [True, False, False], [False, False, False]]}, {'votes': [False, False, False], 'isolated': [0]}), ('control 12', {'isolate_after': 3, 'cycles': [[False, False, False], [False, True, False], [True, False, True], [True, False, True], [False, False, True], [False, False, False], [True, False, True], [True, True, True]]}, {'votes': [False, False, True, True, True, False, True, True], 'isolated': [1]}), ('control 15', {'isolate_after': 3, 'cycles': [[False, False, False], [False, None, False], [True, False, False], [True, None, False]]}, {'votes': [False, False, False, True], 'isolated': []}), ('sampled regression 18', {'isolate_after': 2, 'cycles': [[False, False, False], [None, False, True], [False, False, True], [True, False, False], [True, False, True], [False, False, False], [False, True, None], [False, False, False], [False, False, False]]}, {'votes': [False, True, False, False, True, False, True, False, False], 'isolated': []})], [('regression: dissent interrupted by failure', {'isolate_after': 2, 'cycles': [[True, False, False], [None, False, False], [True, False, False]]}, {'votes': [False, False, False], 'isolated': []}), ('sampled regression 71', {'isolate_after': 2, 'cycles': [[False, False, None], [True, False, True], [False, False, False], [False, True, False]]}, {'votes': [False, True, False, False], 'isolated': []}), ('sampled regression 20', {'isolate_after': 2, 'cycles': [[False, True, False], [True, False, False], [True, False, None], [False, None, False], [False, True, False], [False, None, None]]}, {'votes': [False, False, True, False, False, True], 'isolated': []}), ('boundary: two dissenters in turn', {'isolate_after': 2, 'cycles': [[True, False, False], [True, False, False], [False, True, False], [False, True, False], [False, False, False]]}, {'votes': [False, False, True, True, True], 'isolated': [0, 2]}), ('boundary: isolated channel keeps reporting', {'isolate_after': 1, 'cycles': [[True, False, False], [True, True, False]]}, {'votes': [False, True], 'isolated': [0, 2]}), ('control 23', {'isolate_after': 2, 'cycles': [[True, False, True], [None, False, False], [False, False, False], [False, False, False], [False, False, None], [False, False, False], [True, None, True]]}, {'votes': [True, False, False, False, False, False, True], 'isolated': []}), ('control 26', {'isolate_after': 2, 'cycles': [[True, True, True], [False, False, False], [False, False, True], [False, False, None]]}, {'votes': [True, False, False, False], 'isolated': []}), ('sampled regression 29', {'isolate_after': 2, 'cycles': [[False, False, True], [False, False, False], [False, False, True], [False, True, False], [False, True, True]]}, {'votes': [False, False, False, False, True], 'isolated': []})], [('regression: dissent interrupted by failure', {'isolate_after': 2, 'cycles': [[True, False, False], [None, False, False], [True, False, False]]}, {'votes': [False, False, False], 'isolated': []}), ('sampled regression 9', {'isolate_after': 3, 'cycles': [[None, False, False], [None, True, False], [False, None, None], [False, False, True], [True, None, False], [True, True, True], [None, False, None], [False, False, False], [True, None, False]]}, {'votes': [False, True, True, False, True, True, True, False, True], 'isolated': []}), ('boundary: isolated channel keeps reporting', {'isolate_after': 1, 'cycles': [[True, False, False], [True, True, False]]}, {'votes': [False, True], 'isolated': [0, 2]}), ('boundary: two healthy channels disagree', {'isolate_after': 3, 'cycles': [[True, False, None]]}, {'votes': [True], 'isolated': []}), ('boundary: two healthy channels agree clear', {'isolate_after': 3, 'cycles': [[False, False, None]]}, {'votes': [False], 'isolated': []}), ('sampled regression 34', {'isolate_after': 2, 'cycles': [[True, True, False], [False, True, False], [True, True, True], [True, True, True], [True, False, True], [False, False, False], [True, False, True]]}, {'votes': [True, False, True, True, True, False, True], 'isolated': []}), ('control 37', {'isolate_after': 3, 'cycles': [[True, True, True], [False, False, False], [False, False, False], [False, True, False], [True, False, False], [False, False, False]]}, {'votes': [True, False, False, False, False, False], 'isolated': []}), ('control 40', {'isolate_after': 2, 'cycles': [[True, None, True], [False, False, None], [False, True, False], [False, True, False], [True, True, True], [True, None, False], [None, False, False], [True, True, True]]}, {'votes': [True, False, False, False, True, True, True, True], 'isolated': [1, 2]})], [('regression: dissent interrupted by failure', {'isolate_after': 2, 'cycles': [[True, False, False], [None, False, False], [True, False, False]]}, {'votes': [False, False, False], 'isolated': []}), ('sampled regression 34', {'isolate_after': 2, 'cycles': [[True, True, False], [False, True, False], [True, True, True], [True, True, True], [True, False, True], [False, False, False], [True, False, True]]}, {'votes': [True, False, True, True, True, False, True], 'isolated': []}), ('sampled regression 9', {'isolate_after': 3, 'cycles': [[None, False, False], [None, True, False], [False, None, None], [False, False, True], [True, None, False], [True, True, True], [None, False, None], [False, False, False], [True, None, False]]}, {'votes': [False, True, True, False, True, True, True, False, True], 'isolated': []}), ('boundary: two healthy channels agree clear', {'isolate_after': 3, 'cycles': [[False, False, None]]}, {'votes': [False], 'isolated': []}), ('boundary: single healthy channel says clear', {'isolate_after': 3, 'cycles': [[False, None, None]]}, {'votes': [True], 'isolated': []}), ('sampled regression 45', {'isolate_after': 2, 'cycles': [[True, True, True], [False, False, False], [False, False, False], [False, True, False], [None, True, False], [None, True, False], [True, False, False]]}, {'votes': [True, False, False, False, True, True, True], 'isolated': [2]}), ('sampled regression 48', {'isolate_after': 2, 'cycles': [[False, False, False], [False, False, False], [False, True, True], [True, True, None], [False, True, False], [True, True, True], [False, False, False], [False, False, False], [False, True, False]]}, {'votes': [False, False, True, True, False, True, False, False, False], 'isolated': []}), ('control 51', {'isolate_after': 3, 'cycles': [[False, False, False], [True, False, False], [True, True, True], [True, True, True], [True, True, True], [True, True, True], [True, False, True], [True, False, False], [True, True, True]]}, {'votes': [False, False, True, True, True, True, True, False, True], 'isolated': []})]]
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 fixtureActualExpectedOutcome
regression: dissent interrupted by failure{'isolated': [0], 'votes': [False, False, False]}{'isolated': [], 'votes': [False, False, False]}Failed
sampled regression 10{'isolated': [1], 'votes': [True, True, False, False, False, True, False, True]}{'isolated': [1], 'votes': [True, True, False, False, False, True, False, True]}Passed
sampled regression 9{'isolated': [2], 'votes': [False, True, True, False, True, True, True, False, True]}{'isolated': [], 'votes': [False, True, True, False, True, True, True, False, True]}Failed
boundary: two healthy channels disagree{'isolated': [], 'votes': [True]}{'isolated': [], 'votes': [True]}Passed
boundary: two healthy channels agree clear{'isolated': [], 'votes': [False]}{'isolated': [], 'votes': [False]}Passed
control 1{'isolated': [], 'votes': [False, True, True, False]}{'isolated': [], 'votes': [False, True, True, False]}Passed
control 4{'isolated': [], 'votes': [True, False, False, True, True, True, False, False, True]}{'isolated': [], 'votes': [True, False, False, True, True, True, False, False, True]}Passed
control 7{'isolated': [], 'votes': [False, False, True, True, True, False, True, False]}{'isolated': [], 'votes': [False, False, True, True, True, False, True, False]}Passed

SHA-256 / 00c762741e45943c29acdf362a1c9758edb66609f3ece05a0766ce585bc9e8ba

3 / The verified repair

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

N = 1
observations = []
def solve(x):
    k = x['isolate_after']
    bad = [0, 0, 0]
    iso = [False, False, False]
    votes = []
    for cyc in x['cycles']:
        vals = [None if iso[i] else cyc[i] for i in range(3)]
        healthy = [v for v in vals if v is not None]
        if len(healthy) < 2:
            vote = True
        else:
            t = sum(1 for v in healthy if v)
            f = len(healthy) - t
            vote = t >= f
        votes.append(vote)
        for i in range(3):
            if vals[i] is not None and vals[i] != vote:
                bad[i] += 1
                if bad[i] >= k:
                    iso[i] = True
            else:
                bad[i] = 0
    return {'votes': votes, 'isolated': [i for i in range(3) if iso[i]]}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression: dissent interrupted by failure', {'isolate_after': 2, 'cycles': [[True, False, False], [None, False, False], [True, False, False]]}, {'votes': [False, False, False], 'isolated': []}), ('sampled regression 10', {'isolate_after': 2, 'cycles': [[None, True, False], [False, None, True], [False, False, False], [False, True, False], [False, True, False], [True, True, False], [False, None, False], [True, True, True]]}, {'votes': [True, True, False, False, False, True, False, True], 'isolated': [1]}), ('sampled regression 9', {'isolate_after': 3, 'cycles': [[None, False, False], [None, True, False], [False, None, None], [False, False, True], [True, None, False], [True, True, True], [None, False, None], [False, False, False], [True, None, False]]}, {'votes': [False, True, True, False, True, True, True, False, True], 'isolated': []}), ('boundary: two healthy channels disagree', {'isolate_after': 3, 'cycles': [[True, False, None]]}, {'votes': [True], 'isolated': []}), ('boundary: two healthy channels agree clear', {'isolate_after': 3, 'cycles': [[False, False, None]]}, {'votes': [False], 'isolated': []}), ('control 1', {'isolate_after': 2, 'cycles': [[False, False, False], [True, None, True], [True, True, True], [None, False, False]]}, {'votes': [False, True, True, False], 'isolated': []}), ('control 4', {'isolate_after': 2, 'cycles': [[False, True, True], [False, False, False], [False, False, False], [True, True, False], [True, True, True], [True, False, True], [False, False, False], [False, False, None], [True, True, True]]}, {'votes': [True, False, False, True, True, True, False, False, True], 'isolated': []}), ('control 7', {'isolate_after': 3, 'cycles': [[False, False, True], [False, False, False], [True, True, True], [False, True, True], [True, True, None], [False, False, False], [True, True, True], [False, False, False]]}, {'votes': [False, False, True, True, True, False, True, False], 'isolated': []})], [('regression: dissent interrupted by failure', {'isolate_after': 2, 'cycles': [[True, False, False], [None, False, False], [True, False, False]]}, {'votes': [False, False, False], 'isolated': []}), ('sampled regression 36', {'isolate_after': 3, 'cycles': [[None, True, False], [None, False, False], [False, False, True], [False, False, False], [True, True, False], [True, True, True], [True, True, None], [True, True, True]]}, {'votes': [True, False, False, False, True, True, True, True], 'isolated': []}), ('sampled regression 19', {'isolate_after': 2, 'cycles': [[True, True, True], [True, False, None], [True, False, True], [None, False, False], [True, True, None], [True, False, False], [False, False, True], [True, True, True]]}, {'votes': [True, True, True, True, True, True, True, True], 'isolated': [1]}), ('boundary: single healthy channel says clear', {'isolate_after': 3, 'cycles': [[False, None, None]]}, {'votes': [True], 'isolated': []}), ('boundary: persistent dissenter', {'isolate_after': 2, 'cycles': [[True, False, False], [True, False, False], [False, False, False]]}, {'votes': [False, False, False], 'isolated': [0]}), ('control 12', {'isolate_after': 3, 'cycles': [[False, False, False], [False, True, False], [True, False, True], [True, False, True], [False, False, True], [False, False, False], [True, False, True], [True, True, True]]}, {'votes': [False, False, True, True, True, False, True, True], 'isolated': [1]}), ('control 15', {'isolate_after': 3, 'cycles': [[False, False, False], [False, None, False], [True, False, False], [True, None, False]]}, {'votes': [False, False, False, True], 'isolated': []}), ('sampled regression 18', {'isolate_after': 2, 'cycles': [[False, False, False], [None, False, True], [False, False, True], [True, False, False], [True, False, True], [False, False, False], [False, True, None], [False, False, False], [False, False, False]]}, {'votes': [False, True, False, False, True, False, True, False, False], 'isolated': []})], [('regression: dissent interrupted by failure', {'isolate_after': 2, 'cycles': [[True, False, False], [None, False, False], [True, False, False]]}, {'votes': [False, False, False], 'isolated': []}), ('sampled regression 71', {'isolate_after': 2, 'cycles': [[False, False, None], [True, False, True], [False, False, False], [False, True, False]]}, {'votes': [False, True, False, False], 'isolated': []}), ('sampled regression 20', {'isolate_after': 2, 'cycles': [[False, True, False], [True, False, False], [True, False, None], [False, None, False], [False, True, False], [False, None, None]]}, {'votes': [False, False, True, False, False, True], 'isolated': []}), ('boundary: two dissenters in turn', {'isolate_after': 2, 'cycles': [[True, False, False], [True, False, False], [False, True, False], [False, True, False], [False, False, False]]}, {'votes': [False, False, True, True, True], 'isolated': [0, 2]}), ('boundary: isolated channel keeps reporting', {'isolate_after': 1, 'cycles': [[True, False, False], [True, True, False]]}, {'votes': [False, True], 'isolated': [0, 2]}), ('control 23', {'isolate_after': 2, 'cycles': [[True, False, True], [None, False, False], [False, False, False], [False, False, False], [False, False, None], [False, False, False], [True, None, True]]}, {'votes': [True, False, False, False, False, False, True], 'isolated': []}), ('control 26', {'isolate_after': 2, 'cycles': [[True, True, True], [False, False, False], [False, False, True], [False, False, None]]}, {'votes': [True, False, False, False], 'isolated': []}), ('sampled regression 29', {'isolate_after': 2, 'cycles': [[False, False, True], [False, False, False], [False, False, True], [False, True, False], [False, True, True]]}, {'votes': [False, False, False, False, True], 'isolated': []})], [('regression: dissent interrupted by failure', {'isolate_after': 2, 'cycles': [[True, False, False], [None, False, False], [True, False, False]]}, {'votes': [False, False, False], 'isolated': []}), ('sampled regression 9', {'isolate_after': 3, 'cycles': [[None, False, False], [None, True, False], [False, None, None], [False, False, True], [True, None, False], [True, True, True], [None, False, None], [False, False, False], [True, None, False]]}, {'votes': [False, True, True, False, True, True, True, False, True], 'isolated': []}), ('boundary: isolated channel keeps reporting', {'isolate_after': 1, 'cycles': [[True, False, False], [True, True, False]]}, {'votes': [False, True], 'isolated': [0, 2]}), ('boundary: two healthy channels disagree', {'isolate_after': 3, 'cycles': [[True, False, None]]}, {'votes': [True], 'isolated': []}), ('boundary: two healthy channels agree clear', {'isolate_after': 3, 'cycles': [[False, False, None]]}, {'votes': [False], 'isolated': []}), ('sampled regression 34', {'isolate_after': 2, 'cycles': [[True, True, False], [False, True, False], [True, True, True], [True, True, True], [True, False, True], [False, False, False], [True, False, True]]}, {'votes': [True, False, True, True, True, False, True], 'isolated': []}), ('control 37', {'isolate_after': 3, 'cycles': [[True, True, True], [False, False, False], [False, False, False], [False, True, False], [True, False, False], [False, False, False]]}, {'votes': [True, False, False, False, False, False], 'isolated': []}), ('control 40', {'isolate_after': 2, 'cycles': [[True, None, True], [False, False, None], [False, True, False], [False, True, False], [True, True, True], [True, None, False], [None, False, False], [True, True, True]]}, {'votes': [True, False, False, False, True, True, True, True], 'isolated': [1, 2]})], [('regression: dissent interrupted by failure', {'isolate_after': 2, 'cycles': [[True, False, False], [None, False, False], [True, False, False]]}, {'votes': [False, False, False], 'isolated': []}), ('sampled regression 34', {'isolate_after': 2, 'cycles': [[True, True, False], [False, True, False], [True, True, True], [True, True, True], [True, False, True], [False, False, False], [True, False, True]]}, {'votes': [True, False, True, True, True, False, True], 'isolated': []}), ('sampled regression 9', {'isolate_after': 3, 'cycles': [[None, False, False], [None, True, False], [False, None, None], [False, False, True], [True, None, False], [True, True, True], [None, False, None], [False, False, False], [True, None, False]]}, {'votes': [False, True, True, False, True, True, True, False, True], 'isolated': []}), ('boundary: two healthy channels agree clear', {'isolate_after': 3, 'cycles': [[False, False, None]]}, {'votes': [False], 'isolated': []}), ('boundary: single healthy channel says clear', {'isolate_after': 3, 'cycles': [[False, None, None]]}, {'votes': [True], 'isolated': []}), ('sampled regression 45', {'isolate_after': 2, 'cycles': [[True, True, True], [False, False, False], [False, False, False], [False, True, False], [None, True, False], [None, True, False], [True, False, False]]}, {'votes': [True, False, False, False, True, True, True], 'isolated': [2]}), ('sampled regression 48', {'isolate_after': 2, 'cycles': [[False, False, False], [False, False, False], [False, True, True], [True, True, None], [False, True, False], [True, True, True], [False, False, False], [False, False, False], [False, True, False]]}, {'votes': [False, False, True, True, False, True, False, False, False], 'isolated': []}), ('control 51', {'isolate_after': 3, 'cycles': [[False, False, False], [True, False, False], [True, True, True], [True, True, True], [True, True, True], [True, True, True], [True, False, True], [True, False, False], [True, True, True]]}, {'votes': [False, False, True, True, True, True, True, False, True], 'isolated': []})]]
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 fixtureActualExpectedOutcome
regression: dissent interrupted by failure{'isolated': [], 'votes': [False, False, False]}{'isolated': [], 'votes': [False, False, False]}Passed
sampled regression 10{'isolated': [1], 'votes': [True, True, False, False, False, True, False, True]}{'isolated': [1], 'votes': [True, True, False, False, False, True, False, True]}Passed
sampled regression 9{'isolated': [], 'votes': [False, True, True, False, True, True, True, False, True]}{'isolated': [], 'votes': [False, True, True, False, True, True, True, False, True]}Passed
boundary: two healthy channels disagree{'isolated': [], 'votes': [True]}{'isolated': [], 'votes': [True]}Passed
boundary: two healthy channels agree clear{'isolated': [], 'votes': [False]}{'isolated': [], 'votes': [False]}Passed
control 1{'isolated': [], 'votes': [False, True, True, False]}{'isolated': [], 'votes': [False, True, True, False]}Passed
control 4{'isolated': [], 'votes': [True, False, False, True, True, True, False, False, True]}{'isolated': [], 'votes': [True, False, False, True, True, True, False, False, True]}Passed
control 7{'isolated': [], 'votes': [False, False, True, True, True, False, True, False]}{'isolated': [], 'votes': [False, False, True, True, True, False, True, False]}Passed

SHA-256 / b5774886046f5af10dcd977d59836b0027809f5a10f61310bcdd218a73785003

Verification & scope

Stipulated toy interlocking contract for a bounded teaching model; it makes no claim of conformance to any railway signalling standard and omits real safety cases. 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 2026-09-29T14:47:49.915001+00:00.

Case digest / 3e0fa4198817bd99ce68b72a2bed90fa20c2b928e12475b2d77afa67c77096ec