FA-67131 / Railway interlocking logic / Open access

Train describer berth stepping: empty berth step · case 01

A train stepping from an unlabelled berth loses its description entirely.

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

ROOT CAUSE

An empty source berth steps a blank instead of the unknown description.

VERIFIED REPAIR

Carry ???? when stepping from an empty berth.

Unsuccessful approach: Reusing the destination description for an empty source hides the unknown train.

Case contract

A train describer has berths 0..n-1. interpose writes a headcode, cancel blanks a berth. step i moves the description from berth i to i+1 (or out of the area from the last berth, recorded in exited); stepping an empty berth carries the unknown description ????. Stepping onto a filled berth records a clash at the destination and the stepped description overwrites it. The source berth is always blanked.

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):
    n = x['berths']
    b = [None] * n
    clashes = []
    exited = []
    for ev in x['events']:
        kind = ev[0]
        if kind == 'interpose':
            b[ev[1]] = ev[2]
        elif kind == 'cancel':
            b[ev[1]] = None
        elif kind == 'step':
            i = ev[1]
            tid = b[i]
            b[i] = None
            if i == n - 1:
                exited.append(tid)
            else:
                if b[i + 1] is not None:
                    clashes.append(i + 1)
                b[i + 1] = tid
    return {'berths': b, 'clashes': clashes, 'exited': exited}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression: step from an empty berth', {'berths': 3, 'events': [['step', 0]]}, {'berths': [None, '????', None], 'clashes': [], 'exited': []}), ('sampled regression 3', {'berths': 3, 'events': [['cancel', 0], ['step', 1], ['step', 2], ['interpose', 0, '9Z10'], ['cancel', 1], ['interpose', 2, '9Z10']]}, {'berths': ['9Z10', None, '9Z10'], 'clashes': [], 'exited': ['????']}), ('sampled regression 4', {'berths': 4, 'events': [['step', 1], ['cancel', 0], ['step', 0]]}, {'berths': [None, '????', '????', None], 'clashes': [], 'exited': []}), ('boundary: normal stepping', {'berths': 3, 'events': [['interpose', 0, '1A01'], ['step', 0], ['step', 1]]}, {'berths': [None, None, '1A01'], 'clashes': [], 'exited': []}), ('boundary: exit from the last berth', {'berths': 3, 'events': [['interpose', 1, '2B17'], ['step', 1], ['step', 2]]}, {'berths': [None, None, None], 'clashes': [], 'exited': ['2B17']}), ('sampled regression 1', {'berths': 5, 'events': [['cancel', 1], ['step', 3], ['step', 4], ['step', 1], ['interpose', 1, '1A01'], ['cancel', 2], ['interpose', 0, '2B17'], ['step', 4]]}, {'berths': ['2B17', '1A01', None, None, None], 'clashes': [], 'exited': ['????', '????']}), ('sampled regression 7', {'berths': 4, 'events': [['interpose', 3, '5X99'], ['step', 1], ['step', 1]]}, {'berths': [None, None, '????', '5X99'], 'clashes': [2], 'exited': []}), ('sampled regression 10', {'berths': 3, 'events': [['interpose', 1, '9Z10'], ['interpose', 0, '2B17'], ['step', 1], ['step', 1], ['step', 0], ['step', 0], ['step', 2], ['interpose', 2, '2B17'], ['step', 1]]}, {'berths': [None, None, '????'], 'clashes': [2, 1, 2], 'exited': ['????']})], [('regression: unknown train leaves the area', {'berths': 2, 'events': [['step', 1]]}, {'berths': [None, None], 'clashes': [], 'exited': ['????']}), ('regression: step from an empty berth', {'berths': 3, 'events': [['step', 0]]}, {'berths': [None, '????', None], 'clashes': [], 'exited': []}), ('sampled regression 10', {'berths': 3, 'events': [['interpose', 1, '9Z10'], ['interpose', 0, '2B17'], ['step', 1], ['step', 1], ['step', 0], ['step', 0], ['step', 2], ['interpose', 2, '2B17'], ['step', 1]]}, {'berths': [None, None, '????'], 'clashes': [2, 1, 2], 'exited': ['????']}), ('sampled regression 11', {'berths': 5, 'events': [['step', 1], ['step', 3], ['interpose', 0, '5X99'], ['step', 3], ['interpose', 1, '5X99'], ['step', 1], ['step', 2], ['cancel', 2], ['step', 4]]}, {'berths': ['5X99', None, None, '5X99', None], 'clashes': [4, 2], 'exited': ['????']}), ('boundary: exit from the last berth', {'berths': 3, 'events': [['interpose', 1, '2B17'], ['step', 1], ['step', 2]]}, {'berths': [None, None, None], 'clashes': [], 'exited': ['2B17']}), ('sampled regression 12', {'berths': 3, 'events': [['step', 1], ['interpose', 1, '5X99'], ['cancel', 0], ['cancel', 1], ['step', 2], ['step', 0], ['step', 0]]}, {'berths': [None, '????', None], 'clashes': [1], 'exited': ['????']}), ('sampled regression 15', {'berths': 4, 'events': [['step', 0], ['interpose', 3, '5X99'], ['cancel', 2]]}, {'berths': [None, '????', None, '5X99'], 'clashes': [], 'exited': []}), ('sampled regression 18', {'berths': 3, 'events': [['interpose', 2, '9Z10'], ['cancel', 2], ['step', 0], ['step', 0], ['cancel', 1], ['step', 0], ['step', 1], ['step', 0]]}, {'berths': [None, '????', '????'], 'clashes': [1], 'exited': []})], [('regression: step from an empty berth', {'berths': 3, 'events': [['step', 0]]}, {'berths': [None, '????', None], 'clashes': [], 'exited': []}), ('sampled regression 17', {'berths': 4, 'events': [['step', 3], ['step', 2], ['step', 0], ['interpose', 1, '5X99'], ['step', 1], ['interpose', 2, '9Z10'], ['cancel', 2], ['interpose', 2, '5X99'], ['step', 0]]}, {'berths': [None, '????', '5X99', '????'], 'clashes': [], 'exited': ['????']}), ('sampled regression 16', {'berths': 4, 'events': [['step', 0], ['cancel', 3], ['step', 0], ['interpose', 3, '5X99'], ['interpose', 0, '9Z10'], ['step', 3], ['interpose', 2, '5X99'], ['step', 2]]}, {'berths': ['9Z10', '????', None, '5X99'], 'clashes': [1], 'exited': ['5X99']}), ('boundary: clash with a different train', {'berths': 3, 'events': [['interpose', 0, '1A01'], ['interpose', 1, '2B17'], ['step', 0]]}, {'berths': [None, '1A01', None], 'clashes': [1], 'exited': []}), ('boundary: clash with the same headcode', {'berths': 3, 'events': [['interpose', 0, '1A01'], ['interpose', 1, '1A01'], ['step', 0]]}, {'berths': [None, '1A01', None], 'clashes': [1], 'exited': []}), ('sampled regression 23', {'berths': 3, 'events': [['interpose', 2, '9Z10'], ['step', 1], ['step', 2], ['cancel', 1], ['interpose', 0, '1A01'], ['step', 2]]}, {'berths': ['1A01', None, None], 'clashes': [2], 'exited': ['????', '????']}), ('sampled regression 26', {'berths': 5, 'events': [['step', 1], ['cancel', 3], ['interpose', 4, '5X99'], ['cancel', 2], ['interpose', 1, '9Z10'], ['interpose', 3, '1A01'], ['step', 3], ['step', 2], ['step', 1]]}, {'berths': [None, None, '9Z10', '????', '1A01'], 'clashes': [4], 'exited': []}), ('sampled regression 29', {'berths': 5, 'events': [['interpose', 4, '1A01'], ['cancel', 4], ['step', 1], ['interpose', 1, '2B17'], ['step', 3], ['cancel', 3], ['interpose', 2, '9Z10'], ['step', 1]]}, {'berths': [None, None, '2B17', None, '????'], 'clashes': [2], 'exited': []})], [('regression: unknown train leaves the area', {'berths': 2, 'events': [['step', 1]]}, {'berths': [None, None], 'clashes': [], 'exited': ['????']}), ('regression: step from an empty berth', {'berths': 3, 'events': [['step', 0]]}, {'berths': [None, '????', None], 'clashes': [], 'exited': []}), ('sampled regression 24', {'berths': 4, 'events': [['step', 1], ['cancel', 0], ['step', 3]]}, {'berths': [None, None, '????', None], 'clashes': [], 'exited': ['????']}), ('sampled regression 21', {'berths': 5, 'events': [['step', 3], ['step', 3], ['step', 0], ['step', 1], ['step', 1], ['step', 3], ['step', 1], ['step', 0]]}, {'berths': [None, '????', '????', None, '????'], 'clashes': [4, 2, 4, 2], 'exited': []}), ('boundary: stepping from the penultimate berth', {'berths': 4, 'events': [['interpose', 2, '5X99'], ['step', 2]]}, {'berths': [None, None, None, '5X99'], 'clashes': [], 'exited': []}), ('sampled regression 34', {'berths': 3, 'events': [['step', 2], ['step', 0], ['interpose', 2, '9Z10'], ['step', 1], ['cancel', 1], ['step', 0], ['step', 2]]}, {'berths': [None, '????', None], 'clashes': [2], 'exited': ['????', '????']}), ('sampled regression 37', {'berths': 4, 'events': [['step', 1], ['cancel', 1], ['step', 3], ['interpose', 0, '9Z10']]}, {'berths': ['9Z10', None, '????', None], 'clashes': [], 'exited': ['????']}), ('sampled regression 40', {'berths': 4, 'events': [['step', 3], ['step', 1], ['interpose', 3, '5X99'], ['step', 2], ['interpose', 2, '5X99'], ['step', 3], ['step', 0], ['step', 1]]}, {'berths': [None, None, '????', None], 'clashes': [3, 2], 'exited': ['????', '????']})], [('regression: step from an empty berth', {'berths': 3, 'events': [['step', 0]]}, {'berths': [None, '????', None], 'clashes': [], 'exited': []}), ('sampled regression 32', {'berths': 3, 'events': [['step', 0], ['step', 0], ['interpose', 1, '2B17'], ['step', 1], ['interpose', 2, '5X99'], ['interpose', 1, '2B17'], ['step', 2], ['cancel', 0], ['step', 0]]}, {'berths': [None, '????', None], 'clashes': [1, 1], 'exited': ['5X99']}), ('sampled regression 27', {'berths': 5, 'events': [['step', 2], ['step', 4], ['step', 2], ['step', 2], ['step', 2], ['step', 1], ['cancel', 2], ['step', 4]]}, {'berths': [None, None, None, '????', None], 'clashes': [3, 3, 3], 'exited': ['????', '????']}), ('boundary: normal stepping', {'berths': 3, 'events': [['interpose', 0, '1A01'], ['step', 0], ['step', 1]]}, {'berths': [None, None, '1A01'], 'clashes': [], 'exited': []}), ('boundary: exit from the last berth', {'berths': 3, 'events': [['interpose', 1, '2B17'], ['step', 1], ['step', 2]]}, {'berths': [None, None, None], 'clashes': [], 'exited': ['2B17']}), ('control 45', {'berths': 3, 'events': [['interpose', 0, '9Z10'], ['interpose', 0, '5X99'], ['interpose', 0, '2B17']]}, {'berths': ['2B17', None, None], 'clashes': [], 'exited': []}), ('sampled regression 48', {'berths': 4, 'events': [['step', 2], ['step', 2], ['step', 0], ['step', 0], ['interpose', 0, '9Z10'], ['interpose', 1, '1A01'], ['cancel', 2], ['step', 2]]}, {'berths': ['9Z10', '1A01', None, '????'], 'clashes': [3, 1, 3], 'exited': []}), ('sampled regression 51', {'berths': 3, 'events': [['step', 2], ['step', 2], ['interpose', 1, '5X99'], ['interpose', 1, '9Z10'], ['step', 0], ['step', 0], ['interpose', 2, '9Z10'], ['step', 0], ['step', 0]]}, {'berths': [None, '????', '9Z10'], 'clashes': [1, 1, 1, 1], 'exited': ['????', '????']})]]
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: step from an empty berth	`{'berths': [None, None, None], 'clashes': [], 'exited': []}`	`{'berths': [None, '????', None], 'clashes': [], 'exited': []}`	Failed
sampled regression 3	`{'berths': ['9Z10', None, '9Z10'], 'clashes': [], 'exited': [None]}`	`{'berths': ['9Z10', None, '9Z10'], 'clashes': [], 'exited': ['????']}`	Failed
sampled regression 4	`{'berths': [None, None, None, None], 'clashes': [], 'exited': []}`	`{'berths': [None, '????', '????', None], 'clashes': [], 'exited': []}`	Failed
boundary: normal stepping	`{'berths': [None, None, '1A01'], 'clashes': [], 'exited': []}`	`{'berths': [None, None, '1A01'], 'clashes': [], 'exited': []}`	Passed
boundary: exit from the last berth	`{'berths': [None, None, None], 'clashes': [], 'exited': ['2B17']}`	`{'berths': [None, None, None], 'clashes': [], 'exited': ['2B17']}`	Passed
sampled regression 1	`{'berths': ['2B17', '1A01', None, None, None], 'clashes': [], 'exited': [None, None]}`	`{'berths': ['2B17', '1A01', None, None, None], 'clashes': [], 'exited': ['????', '????']}`	Failed
sampled regression 7	`{'berths': [None, None, None, '5X99'], 'clashes': [], 'exited': []}`	`{'berths': [None, None, '????', '5X99'], 'clashes': [2], 'exited': []}`	Failed
sampled regression 10	`{'berths': [None, None, None], 'clashes': [2, 1, 2], 'exited': [None]}`	`{'berths': [None, None, '????'], 'clashes': [2, 1, 2], 'exited': ['????']}`	Failed

SHA-256 / 7934dd24169c6e5fda261a1091b45c73f2609d8e4080e06fed5df017218135a9

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(x):
    n = x['berths']
    b = [None] * n
    clashes = []
    exited = []
    for ev in x['events']:
        kind = ev[0]
        if kind == 'interpose':
            b[ev[1]] = ev[2]
        elif kind == 'cancel':
            b[ev[1]] = None
        elif kind == 'step':
            i = ev[1]
            tid = b[i] if b[i] is not None else b[i + 1] if i + 1 < n else '????'
            b[i] = None
            if i == n - 1:
                exited.append(tid)
            else:
                if b[i + 1] is not None:
                    clashes.append(i + 1)
                b[i + 1] = tid
    return {'berths': b, 'clashes': clashes, 'exited': exited}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression: step from an empty berth', {'berths': 3, 'events': [['step', 0]]}, {'berths': [None, '????', None], 'clashes': [], 'exited': []}), ('sampled regression 3', {'berths': 3, 'events': [['cancel', 0], ['step', 1], ['step', 2], ['interpose', 0, '9Z10'], ['cancel', 1], ['interpose', 2, '9Z10']]}, {'berths': ['9Z10', None, '9Z10'], 'clashes': [], 'exited': ['????']}), ('sampled regression 4', {'berths': 4, 'events': [['step', 1], ['cancel', 0], ['step', 0]]}, {'berths': [None, '????', '????', None], 'clashes': [], 'exited': []}), ('boundary: normal stepping', {'berths': 3, 'events': [['interpose', 0, '1A01'], ['step', 0], ['step', 1]]}, {'berths': [None, None, '1A01'], 'clashes': [], 'exited': []}), ('boundary: exit from the last berth', {'berths': 3, 'events': [['interpose', 1, '2B17'], ['step', 1], ['step', 2]]}, {'berths': [None, None, None], 'clashes': [], 'exited': ['2B17']}), ('sampled regression 1', {'berths': 5, 'events': [['cancel', 1], ['step', 3], ['step', 4], ['step', 1], ['interpose', 1, '1A01'], ['cancel', 2], ['interpose', 0, '2B17'], ['step', 4]]}, {'berths': ['2B17', '1A01', None, None, None], 'clashes': [], 'exited': ['????', '????']}), ('sampled regression 7', {'berths': 4, 'events': [['interpose', 3, '5X99'], ['step', 1], ['step', 1]]}, {'berths': [None, None, '????', '5X99'], 'clashes': [2], 'exited': []}), ('sampled regression 10', {'berths': 3, 'events': [['interpose', 1, '9Z10'], ['interpose', 0, '2B17'], ['step', 1], ['step', 1], ['step', 0], ['step', 0], ['step', 2], ['interpose', 2, '2B17'], ['step', 1]]}, {'berths': [None, None, '????'], 'clashes': [2, 1, 2], 'exited': ['????']})], [('regression: unknown train leaves the area', {'berths': 2, 'events': [['step', 1]]}, {'berths': [None, None], 'clashes': [], 'exited': ['????']}), ('regression: step from an empty berth', {'berths': 3, 'events': [['step', 0]]}, {'berths': [None, '????', None], 'clashes': [], 'exited': []}), ('sampled regression 10', {'berths': 3, 'events': [['interpose', 1, '9Z10'], ['interpose', 0, '2B17'], ['step', 1], ['step', 1], ['step', 0], ['step', 0], ['step', 2], ['interpose', 2, '2B17'], ['step', 1]]}, {'berths': [None, None, '????'], 'clashes': [2, 1, 2], 'exited': ['????']}), ('sampled regression 11', {'berths': 5, 'events': [['step', 1], ['step', 3], ['interpose', 0, '5X99'], ['step', 3], ['interpose', 1, '5X99'], ['step', 1], ['step', 2], ['cancel', 2], ['step', 4]]}, {'berths': ['5X99', None, None, '5X99', None], 'clashes': [4, 2], 'exited': ['????']}), ('boundary: exit from the last berth', {'berths': 3, 'events': [['interpose', 1, '2B17'], ['step', 1], ['step', 2]]}, {'berths': [None, None, None], 'clashes': [], 'exited': ['2B17']}), ('sampled regression 12', {'berths': 3, 'events': [['step', 1], ['interpose', 1, '5X99'], ['cancel', 0], ['cancel', 1], ['step', 2], ['step', 0], ['step', 0]]}, {'berths': [None, '????', None], 'clashes': [1], 'exited': ['????']}), ('sampled regression 15', {'berths': 4, 'events': [['step', 0], ['interpose', 3, '5X99'], ['cancel', 2]]}, {'berths': [None, '????', None, '5X99'], 'clashes': [], 'exited': []}), ('sampled regression 18', {'berths': 3, 'events': [['interpose', 2, '9Z10'], ['cancel', 2], ['step', 0], ['step', 0], ['cancel', 1], ['step', 0], ['step', 1], ['step', 0]]}, {'berths': [None, '????', '????'], 'clashes': [1], 'exited': []})], [('regression: step from an empty berth', {'berths': 3, 'events': [['step', 0]]}, {'berths': [None, '????', None], 'clashes': [], 'exited': []}), ('sampled regression 17', {'berths': 4, 'events': [['step', 3], ['step', 2], ['step', 0], ['interpose', 1, '5X99'], ['step', 1], ['interpose', 2, '9Z10'], ['cancel', 2], ['interpose', 2, '5X99'], ['step', 0]]}, {'berths': [None, '????', '5X99', '????'], 'clashes': [], 'exited': ['????']}), ('sampled regression 16', {'berths': 4, 'events': [['step', 0], ['cancel', 3], ['step', 0], ['interpose', 3, '5X99'], ['interpose', 0, '9Z10'], ['step', 3], ['interpose', 2, '5X99'], ['step', 2]]}, {'berths': ['9Z10', '????', None, '5X99'], 'clashes': [1], 'exited': ['5X99']}), ('boundary: clash with a different train', {'berths': 3, 'events': [['interpose', 0, '1A01'], ['interpose', 1, '2B17'], ['step', 0]]}, {'berths': [None, '1A01', None], 'clashes': [1], 'exited': []}), ('boundary: clash with the same headcode', {'berths': 3, 'events': [['interpose', 0, '1A01'], ['interpose', 1, '1A01'], ['step', 0]]}, {'berths': [None, '1A01', None], 'clashes': [1], 'exited': []}), ('sampled regression 23', {'berths': 3, 'events': [['interpose', 2, '9Z10'], ['step', 1], ['step', 2], ['cancel', 1], ['interpose', 0, '1A01'], ['step', 2]]}, {'berths': ['1A01', None, None], 'clashes': [2], 'exited': ['????', '????']}), ('sampled regression 26', {'berths': 5, 'events': [['step', 1], ['cancel', 3], ['interpose', 4, '5X99'], ['cancel', 2], ['interpose', 1, '9Z10'], ['interpose', 3, '1A01'], ['step', 3], ['step', 2], ['step', 1]]}, {'berths': [None, None, '9Z10', '????', '1A01'], 'clashes': [4], 'exited': []}), ('sampled regression 29', {'berths': 5, 'events': [['interpose', 4, '1A01'], ['cancel', 4], ['step', 1], ['interpose', 1, '2B17'], ['step', 3], ['cancel', 3], ['interpose', 2, '9Z10'], ['step', 1]]}, {'berths': [None, None, '2B17', None, '????'], 'clashes': [2], 'exited': []})], [('regression: unknown train leaves the area', {'berths': 2, 'events': [['step', 1]]}, {'berths': [None, None], 'clashes': [], 'exited': ['????']}), ('regression: step from an empty berth', {'berths': 3, 'events': [['step', 0]]}, {'berths': [None, '????', None], 'clashes': [], 'exited': []}), ('sampled regression 24', {'berths': 4, 'events': [['step', 1], ['cancel', 0], ['step', 3]]}, {'berths': [None, None, '????', None], 'clashes': [], 'exited': ['????']}), ('sampled regression 21', {'berths': 5, 'events': [['step', 3], ['step', 3], ['step', 0], ['step', 1], ['step', 1], ['step', 3], ['step', 1], ['step', 0]]}, {'berths': [None, '????', '????', None, '????'], 'clashes': [4, 2, 4, 2], 'exited': []}), ('boundary: stepping from the penultimate berth', {'berths': 4, 'events': [['interpose', 2, '5X99'], ['step', 2]]}, {'berths': [None, None, None, '5X99'], 'clashes': [], 'exited': []}), ('sampled regression 34', {'berths': 3, 'events': [['step', 2], ['step', 0], ['interpose', 2, '9Z10'], ['step', 1], ['cancel', 1], ['step', 0], ['step', 2]]}, {'berths': [None, '????', None], 'clashes': [2], 'exited': ['????', '????']}), ('sampled regression 37', {'berths': 4, 'events': [['step', 1], ['cancel', 1], ['step', 3], ['interpose', 0, '9Z10']]}, {'berths': ['9Z10', None, '????', None], 'clashes': [], 'exited': ['????']}), ('sampled regression 40', {'berths': 4, 'events': [['step', 3], ['step', 1], ['interpose', 3, '5X99'], ['step', 2], ['interpose', 2, '5X99'], ['step', 3], ['step', 0], ['step', 1]]}, {'berths': [None, None, '????', None], 'clashes': [3, 2], 'exited': ['????', '????']})], [('regression: step from an empty berth', {'berths': 3, 'events': [['step', 0]]}, {'berths': [None, '????', None], 'clashes': [], 'exited': []}), ('sampled regression 32', {'berths': 3, 'events': [['step', 0], ['step', 0], ['interpose', 1, '2B17'], ['step', 1], ['interpose', 2, '5X99'], ['interpose', 1, '2B17'], ['step', 2], ['cancel', 0], ['step', 0]]}, {'berths': [None, '????', None], 'clashes': [1, 1], 'exited': ['5X99']}), ('sampled regression 27', {'berths': 5, 'events': [['step', 2], ['step', 4], ['step', 2], ['step', 2], ['step', 2], ['step', 1], ['cancel', 2], ['step', 4]]}, {'berths': [None, None, None, '????', None], 'clashes': [3, 3, 3], 'exited': ['????', '????']}), ('boundary: normal stepping', {'berths': 3, 'events': [['interpose', 0, '1A01'], ['step', 0], ['step', 1]]}, {'berths': [None, None, '1A01'], 'clashes': [], 'exited': []}), ('boundary: exit from the last berth', {'berths': 3, 'events': [['interpose', 1, '2B17'], ['step', 1], ['step', 2]]}, {'berths': [None, None, None], 'clashes': [], 'exited': ['2B17']}), ('control 45', {'berths': 3, 'events': [['interpose', 0, '9Z10'], ['interpose', 0, '5X99'], ['interpose', 0, '2B17']]}, {'berths': ['2B17', None, None], 'clashes': [], 'exited': []}), ('sampled regression 48', {'berths': 4, 'events': [['step', 2], ['step', 2], ['step', 0], ['step', 0], ['interpose', 0, '9Z10'], ['interpose', 1, '1A01'], ['cancel', 2], ['step', 2]]}, {'berths': ['9Z10', '1A01', None, '????'], 'clashes': [3, 1, 3], 'exited': []}), ('sampled regression 51', {'berths': 3, 'events': [['step', 2], ['step', 2], ['interpose', 1, '5X99'], ['interpose', 1, '9Z10'], ['step', 0], ['step', 0], ['interpose', 2, '9Z10'], ['step', 0], ['step', 0]]}, {'berths': [None, '????', '9Z10'], 'clashes': [1, 1, 1, 1], 'exited': ['????', '????']})]]
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: step from an empty berth	`{'berths': [None, None, None], 'clashes': [], 'exited': []}`	`{'berths': [None, '????', None], 'clashes': [], 'exited': []}`	Failed
sampled regression 3	`{'berths': ['9Z10', None, '9Z10'], 'clashes': [], 'exited': ['????']}`	`{'berths': ['9Z10', None, '9Z10'], 'clashes': [], 'exited': ['????']}`	Passed
sampled regression 4	`{'berths': [None, None, None, None], 'clashes': [], 'exited': []}`	`{'berths': [None, '????', '????', None], 'clashes': [], 'exited': []}`	Failed
boundary: normal stepping	`{'berths': [None, None, '1A01'], 'clashes': [], 'exited': []}`	`{'berths': [None, None, '1A01'], 'clashes': [], 'exited': []}`	Passed
boundary: exit from the last berth	`{'berths': [None, None, None], 'clashes': [], 'exited': ['2B17']}`	`{'berths': [None, None, None], 'clashes': [], 'exited': ['2B17']}`	Passed
sampled regression 1	`{'berths': ['2B17', '1A01', None, None, None], 'clashes': [], 'exited': ['????', '????']}`	`{'berths': ['2B17', '1A01', None, None, None], 'clashes': [], 'exited': ['????', '????']}`	Passed
sampled regression 7	`{'berths': [None, None, None, '5X99'], 'clashes': [], 'exited': []}`	`{'berths': [None, None, '????', '5X99'], 'clashes': [2], 'exited': []}`	Failed
sampled regression 10	`{'berths': [None, None, '2B17'], 'clashes': [2, 1, 2], 'exited': ['9Z10']}`	`{'berths': [None, None, '????'], 'clashes': [2, 1, 2], 'exited': ['????']}`	Failed

SHA-256 / 288f538163ac1da6caf6dea6360949fe183facbd5426ba5419912dfa18aeafbe

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(x):
    n = x['berths']
    b = [None] * n
    clashes = []
    exited = []
    for ev in x['events']:
        kind = ev[0]
        if kind == 'interpose':
            b[ev[1]] = ev[2]
        elif kind == 'cancel':
            b[ev[1]] = None
        elif kind == 'step':
            i = ev[1]
            tid = b[i] if b[i] is not None else '????'
            b[i] = None
            if i == n - 1:
                exited.append(tid)
            else:
                if b[i + 1] is not None:
                    clashes.append(i + 1)
                b[i + 1] = tid
    return {'berths': b, 'clashes': clashes, 'exited': exited}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression: step from an empty berth', {'berths': 3, 'events': [['step', 0]]}, {'berths': [None, '????', None], 'clashes': [], 'exited': []}), ('sampled regression 3', {'berths': 3, 'events': [['cancel', 0], ['step', 1], ['step', 2], ['interpose', 0, '9Z10'], ['cancel', 1], ['interpose', 2, '9Z10']]}, {'berths': ['9Z10', None, '9Z10'], 'clashes': [], 'exited': ['????']}), ('sampled regression 4', {'berths': 4, 'events': [['step', 1], ['cancel', 0], ['step', 0]]}, {'berths': [None, '????', '????', None], 'clashes': [], 'exited': []}), ('boundary: normal stepping', {'berths': 3, 'events': [['interpose', 0, '1A01'], ['step', 0], ['step', 1]]}, {'berths': [None, None, '1A01'], 'clashes': [], 'exited': []}), ('boundary: exit from the last berth', {'berths': 3, 'events': [['interpose', 1, '2B17'], ['step', 1], ['step', 2]]}, {'berths': [None, None, None], 'clashes': [], 'exited': ['2B17']}), ('sampled regression 1', {'berths': 5, 'events': [['cancel', 1], ['step', 3], ['step', 4], ['step', 1], ['interpose', 1, '1A01'], ['cancel', 2], ['interpose', 0, '2B17'], ['step', 4]]}, {'berths': ['2B17', '1A01', None, None, None], 'clashes': [], 'exited': ['????', '????']}), ('sampled regression 7', {'berths': 4, 'events': [['interpose', 3, '5X99'], ['step', 1], ['step', 1]]}, {'berths': [None, None, '????', '5X99'], 'clashes': [2], 'exited': []}), ('sampled regression 10', {'berths': 3, 'events': [['interpose', 1, '9Z10'], ['interpose', 0, '2B17'], ['step', 1], ['step', 1], ['step', 0], ['step', 0], ['step', 2], ['interpose', 2, '2B17'], ['step', 1]]}, {'berths': [None, None, '????'], 'clashes': [2, 1, 2], 'exited': ['????']})], [('regression: unknown train leaves the area', {'berths': 2, 'events': [['step', 1]]}, {'berths': [None, None], 'clashes': [], 'exited': ['????']}), ('regression: step from an empty berth', {'berths': 3, 'events': [['step', 0]]}, {'berths': [None, '????', None], 'clashes': [], 'exited': []}), ('sampled regression 10', {'berths': 3, 'events': [['interpose', 1, '9Z10'], ['interpose', 0, '2B17'], ['step', 1], ['step', 1], ['step', 0], ['step', 0], ['step', 2], ['interpose', 2, '2B17'], ['step', 1]]}, {'berths': [None, None, '????'], 'clashes': [2, 1, 2], 'exited': ['????']}), ('sampled regression 11', {'berths': 5, 'events': [['step', 1], ['step', 3], ['interpose', 0, '5X99'], ['step', 3], ['interpose', 1, '5X99'], ['step', 1], ['step', 2], ['cancel', 2], ['step', 4]]}, {'berths': ['5X99', None, None, '5X99', None], 'clashes': [4, 2], 'exited': ['????']}), ('boundary: exit from the last berth', {'berths': 3, 'events': [['interpose', 1, '2B17'], ['step', 1], ['step', 2]]}, {'berths': [None, None, None], 'clashes': [], 'exited': ['2B17']}), ('sampled regression 12', {'berths': 3, 'events': [['step', 1], ['interpose', 1, '5X99'], ['cancel', 0], ['cancel', 1], ['step', 2], ['step', 0], ['step', 0]]}, {'berths': [None, '????', None], 'clashes': [1], 'exited': ['????']}), ('sampled regression 15', {'berths': 4, 'events': [['step', 0], ['interpose', 3, '5X99'], ['cancel', 2]]}, {'berths': [None, '????', None, '5X99'], 'clashes': [], 'exited': []}), ('sampled regression 18', {'berths': 3, 'events': [['interpose', 2, '9Z10'], ['cancel', 2], ['step', 0], ['step', 0], ['cancel', 1], ['step', 0], ['step', 1], ['step', 0]]}, {'berths': [None, '????', '????'], 'clashes': [1], 'exited': []})], [('regression: step from an empty berth', {'berths': 3, 'events': [['step', 0]]}, {'berths': [None, '????', None], 'clashes': [], 'exited': []}), ('sampled regression 17', {'berths': 4, 'events': [['step', 3], ['step', 2], ['step', 0], ['interpose', 1, '5X99'], ['step', 1], ['interpose', 2, '9Z10'], ['cancel', 2], ['interpose', 2, '5X99'], ['step', 0]]}, {'berths': [None, '????', '5X99', '????'], 'clashes': [], 'exited': ['????']}), ('sampled regression 16', {'berths': 4, 'events': [['step', 0], ['cancel', 3], ['step', 0], ['interpose', 3, '5X99'], ['interpose', 0, '9Z10'], ['step', 3], ['interpose', 2, '5X99'], ['step', 2]]}, {'berths': ['9Z10', '????', None, '5X99'], 'clashes': [1], 'exited': ['5X99']}), ('boundary: clash with a different train', {'berths': 3, 'events': [['interpose', 0, '1A01'], ['interpose', 1, '2B17'], ['step', 0]]}, {'berths': [None, '1A01', None], 'clashes': [1], 'exited': []}), ('boundary: clash with the same headcode', {'berths': 3, 'events': [['interpose', 0, '1A01'], ['interpose', 1, '1A01'], ['step', 0]]}, {'berths': [None, '1A01', None], 'clashes': [1], 'exited': []}), ('sampled regression 23', {'berths': 3, 'events': [['interpose', 2, '9Z10'], ['step', 1], ['step', 2], ['cancel', 1], ['interpose', 0, '1A01'], ['step', 2]]}, {'berths': ['1A01', None, None], 'clashes': [2], 'exited': ['????', '????']}), ('sampled regression 26', {'berths': 5, 'events': [['step', 1], ['cancel', 3], ['interpose', 4, '5X99'], ['cancel', 2], ['interpose', 1, '9Z10'], ['interpose', 3, '1A01'], ['step', 3], ['step', 2], ['step', 1]]}, {'berths': [None, None, '9Z10', '????', '1A01'], 'clashes': [4], 'exited': []}), ('sampled regression 29', {'berths': 5, 'events': [['interpose', 4, '1A01'], ['cancel', 4], ['step', 1], ['interpose', 1, '2B17'], ['step', 3], ['cancel', 3], ['interpose', 2, '9Z10'], ['step', 1]]}, {'berths': [None, None, '2B17', None, '????'], 'clashes': [2], 'exited': []})], [('regression: unknown train leaves the area', {'berths': 2, 'events': [['step', 1]]}, {'berths': [None, None], 'clashes': [], 'exited': ['????']}), ('regression: step from an empty berth', {'berths': 3, 'events': [['step', 0]]}, {'berths': [None, '????', None], 'clashes': [], 'exited': []}), ('sampled regression 24', {'berths': 4, 'events': [['step', 1], ['cancel', 0], ['step', 3]]}, {'berths': [None, None, '????', None], 'clashes': [], 'exited': ['????']}), ('sampled regression 21', {'berths': 5, 'events': [['step', 3], ['step', 3], ['step', 0], ['step', 1], ['step', 1], ['step', 3], ['step', 1], ['step', 0]]}, {'berths': [None, '????', '????', None, '????'], 'clashes': [4, 2, 4, 2], 'exited': []}), ('boundary: stepping from the penultimate berth', {'berths': 4, 'events': [['interpose', 2, '5X99'], ['step', 2]]}, {'berths': [None, None, None, '5X99'], 'clashes': [], 'exited': []}), ('sampled regression 34', {'berths': 3, 'events': [['step', 2], ['step', 0], ['interpose', 2, '9Z10'], ['step', 1], ['cancel', 1], ['step', 0], ['step', 2]]}, {'berths': [None, '????', None], 'clashes': [2], 'exited': ['????', '????']}), ('sampled regression 37', {'berths': 4, 'events': [['step', 1], ['cancel', 1], ['step', 3], ['interpose', 0, '9Z10']]}, {'berths': ['9Z10', None, '????', None], 'clashes': [], 'exited': ['????']}), ('sampled regression 40', {'berths': 4, 'events': [['step', 3], ['step', 1], ['interpose', 3, '5X99'], ['step', 2], ['interpose', 2, '5X99'], ['step', 3], ['step', 0], ['step', 1]]}, {'berths': [None, None, '????', None], 'clashes': [3, 2], 'exited': ['????', '????']})], [('regression: step from an empty berth', {'berths': 3, 'events': [['step', 0]]}, {'berths': [None, '????', None], 'clashes': [], 'exited': []}), ('sampled regression 32', {'berths': 3, 'events': [['step', 0], ['step', 0], ['interpose', 1, '2B17'], ['step', 1], ['interpose', 2, '5X99'], ['interpose', 1, '2B17'], ['step', 2], ['cancel', 0], ['step', 0]]}, {'berths': [None, '????', None], 'clashes': [1, 1], 'exited': ['5X99']}), ('sampled regression 27', {'berths': 5, 'events': [['step', 2], ['step', 4], ['step', 2], ['step', 2], ['step', 2], ['step', 1], ['cancel', 2], ['step', 4]]}, {'berths': [None, None, None, '????', None], 'clashes': [3, 3, 3], 'exited': ['????', '????']}), ('boundary: normal stepping', {'berths': 3, 'events': [['interpose', 0, '1A01'], ['step', 0], ['step', 1]]}, {'berths': [None, None, '1A01'], 'clashes': [], 'exited': []}), ('boundary: exit from the last berth', {'berths': 3, 'events': [['interpose', 1, '2B17'], ['step', 1], ['step', 2]]}, {'berths': [None, None, None], 'clashes': [], 'exited': ['2B17']}), ('control 45', {'berths': 3, 'events': [['interpose', 0, '9Z10'], ['interpose', 0, '5X99'], ['interpose', 0, '2B17']]}, {'berths': ['2B17', None, None], 'clashes': [], 'exited': []}), ('sampled regression 48', {'berths': 4, 'events': [['step', 2], ['step', 2], ['step', 0], ['step', 0], ['interpose', 0, '9Z10'], ['interpose', 1, '1A01'], ['cancel', 2], ['step', 2]]}, {'berths': ['9Z10', '1A01', None, '????'], 'clashes': [3, 1, 3], 'exited': []}), ('sampled regression 51', {'berths': 3, 'events': [['step', 2], ['step', 2], ['interpose', 1, '5X99'], ['interpose', 1, '9Z10'], ['step', 0], ['step', 0], ['interpose', 2, '9Z10'], ['step', 0], ['step', 0]]}, {'berths': [None, '????', '9Z10'], 'clashes': [1, 1, 1, 1], 'exited': ['????', '????']})]]
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: step from an empty berth	`{'berths': [None, '????', None], 'clashes': [], 'exited': []}`	`{'berths': [None, '????', None], 'clashes': [], 'exited': []}`	Passed
sampled regression 3	`{'berths': ['9Z10', None, '9Z10'], 'clashes': [], 'exited': ['????']}`	`{'berths': ['9Z10', None, '9Z10'], 'clashes': [], 'exited': ['????']}`	Passed
sampled regression 4	`{'berths': [None, '????', '????', None], 'clashes': [], 'exited': []}`	`{'berths': [None, '????', '????', None], 'clashes': [], 'exited': []}`	Passed
boundary: normal stepping	`{'berths': [None, None, '1A01'], 'clashes': [], 'exited': []}`	`{'berths': [None, None, '1A01'], 'clashes': [], 'exited': []}`	Passed
boundary: exit from the last berth	`{'berths': [None, None, None], 'clashes': [], 'exited': ['2B17']}`	`{'berths': [None, None, None], 'clashes': [], 'exited': ['2B17']}`	Passed
sampled regression 1	`{'berths': ['2B17', '1A01', None, None, None], 'clashes': [], 'exited': ['????', '????']}`	`{'berths': ['2B17', '1A01', None, None, None], 'clashes': [], 'exited': ['????', '????']}`	Passed
sampled regression 7	`{'berths': [None, None, '????', '5X99'], 'clashes': [2], 'exited': []}`	`{'berths': [None, None, '????', '5X99'], 'clashes': [2], 'exited': []}`	Passed
sampled regression 10	`{'berths': [None, None, '????'], 'clashes': [2, 1, 2], 'exited': ['????']}`	`{'berths': [None, None, '????'], 'clashes': [2, 1, 2], 'exited': ['????']}`	Passed

SHA-256 / dfaba2dfc40586497f711f3e77735e515784a506dcd1dc7f65355f429998d27c

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 2026-09-29T14:47:50.028751+00:00.

Case digest / 272e2c974e56665afb1a24909d09ca971a3d7a287f3630de39bb99aa7446684b