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FA-89096 / Digital logic simulation / Open access

Missing transition returns to the start state · case 01

An input with no listed transition resets the machine instead of holding its state.

Verified by executionVariant 1 · 7 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The default next state for an absent transition is the start state.

THE FAILURE

The default next state for an absent transition is the start state.

Unsuccessful approach: Treating an absent transition as unknown poisons a legal hold.

Case contract

Input [table, start, stream]: table[state] = {'out': o, 'next': {bit: state}}; stream items are [bit, rst] with bit 0/1/'x'. Each cycle outputs the current state's output (or 'x' in the unknown state 'X'), then clocks: rst==1 -> start (synchronous), else unknown input or state 'X' -> 'X', else follow next[bit], staying put if that transition is absent. Return [outputs, final state].

Why this case matters

Cycle-based simulators must emit Moore outputs from the pre-edge state and model unknown propagation through state registers.

1 / The failure

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

N = 1
observations = []
def solve(*args):
    table, start, stream = args
    state = start
    outs = []
    for bit, rst in stream:
        o = 'x' if state == 'X' else table[state]['out']
        if rst == 1:
            state = start
        elif state == 'X' or bit == 'x':
            state = 'X'
        else:
            state = table[state]['next'].get(str(bit), start)
        outs.append(o)
    return [outs, state]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('detects two ones', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [0, 0], [1, 0], [0, 0]]], [[0, 0, 1, 0, 0], 'A']), ('reset while in output state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [1, 1], [1, 0], [1, 0]]], [[0, 0, 1, 0, 0], 'C']), ('missing transition holds state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [1, 0], [0, 0]]], [[0, 0, 1, 1], 'A']), ('unknown input poisons state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], ['x', 0], [1, 0], [0, 0], [0, 1], [1, 0]]], [[0, 0, 'x', 'x', 'x', 0], 'B']), ('reset from unknown state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'B', [['x', 0], [0, 1], [1, 0]]], [[0, 'x', 0], 'C']), ('reset asserted in first cycle', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 1], [1, 0], [1, 0], [0, 0]]], [[0, 0, 0, 1], 'A']), ('start in accepting state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'C', [[1, 0], [0, 0], [1, 0]]], [[1, 1, 0], 'B'])], [('detects two ones', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [0, 0], [1, 0], [0, 0], [0, 0]]], [[0, 0, 1, 0, 0, 0], 'A']), ('reset while in output state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [1, 1], [1, 0], [1, 0], [1, 0]]], [[0, 0, 1, 0, 0, 1], 'C']), ('missing transition holds state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [1, 0], [1, 0], [0, 0]]], [[0, 0, 1, 1, 1], 'A']), ('unknown input poisons state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], ['x', 0], [1, 0], [0, 0], [0, 0], [0, 1], [1, 0]]], [[0, 0, 'x', 'x', 'x', 'x', 0], 'B']), ('reset from unknown state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'B', [['x', 0], [0, 1], [1, 0], [1, 0]]], [[0, 'x', 0, 1], 'C']), ('reset asserted in first cycle', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 1], [1, 0], [1, 0]]], [[0, 0, 0], 'C']), ('start in accepting state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'C', [[1, 0], [1, 0], [0, 0], [1, 0]]], [[1, 1, 1, 0], 'B'])], [('detects two ones', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [0, 0], [1, 0], [0, 0], [0, 0], [0, 0]]], [[0, 0, 1, 0, 0, 0, 0], 'A']), ('reset while in output state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [1, 1], [1, 0], [1, 0], [1, 0], [1, 0]]], [[0, 0, 1, 0, 0, 1, 1], 'C']), ('missing transition holds state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [1, 0], [1, 0], [1, 0], [0, 0]]], [[0, 0, 1, 1, 1, 1], 'A']), ('unknown input poisons state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], ['x', 0], [1, 0], [0, 0], [0, 0], [0, 0], [0, 1], [1, 0]]], [[0, 0, 'x', 'x', 'x', 'x', 'x', 0], 'B']), ('reset from unknown state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'B', [['x', 0], [0, 1], [1, 0], [1, 0], [1, 0]]], [[0, 'x', 0, 1, 1], 'C']), ('reset asserted in first cycle', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 1], [1, 0], [1, 0], [0, 0]]], [[0, 0, 0, 1], 'A']), ('start in accepting state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'C', [[1, 0], [1, 0], [1, 0], [0, 0], [1, 0]]], [[1, 1, 1, 1, 0], 'B'])], [('detects two ones', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [0, 0], [1, 0], [0, 0], [0, 0], [0, 0], [0, 0]]], [[0, 0, 1, 0, 0, 0, 0, 0], 'A']), ('reset while in output state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [1, 1], [1, 0], [1, 0], [1, 0], [1, 0], [1, 0]]], [[0, 0, 1, 0, 0, 1, 1, 1], 'C']), ('missing transition holds state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [1, 0], [1, 0], [1, 0], [1, 0], [0, 0]]], [[0, 0, 1, 1, 1, 1, 1], 'A']), ('unknown input poisons state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], ['x', 0], [1, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 1], [1, 0]]], [[0, 0, 'x', 'x', 'x', 'x', 'x', 'x', 0], 'B']), ('reset from unknown state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'B', [['x', 0], [0, 1], [1, 0], [1, 0], [1, 0], [1, 0]]], [[0, 'x', 0, 1, 1, 1], 'C']), ('reset asserted in first cycle', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 1], [1, 0], [1, 0]]], [[0, 0, 0], 'C']), ('start in accepting state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'C', [[1, 0], [1, 0], [1, 0], [1, 0], [0, 0], [1, 0]]], [[1, 1, 1, 1, 1, 0], 'B'])], [('detects two ones', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [0, 0], [1, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0]]], [[0, 0, 1, 0, 0, 0, 0, 0, 0], 'A']), ('reset while in output state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [1, 1], [1, 0], [1, 0], [1, 0], [1, 0], [1, 0], [1, 0]]], [[0, 0, 1, 0, 0, 1, 1, 1, 1], 'C']), ('missing transition holds state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [1, 0], [1, 0], [1, 0], [1, 0], [1, 0], [0, 0]]], [[0, 0, 1, 1, 1, 1, 1, 1], 'A']), ('unknown input poisons state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], ['x', 0], [1, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 1], [1, 0]]], [[0, 0, 'x', 'x', 'x', 'x', 'x', 'x', 'x', 0], 'B']), ('reset from unknown state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'B', [['x', 0], [0, 1], [1, 0], [1, 0], [1, 0], [1, 0], [1, 0]]], [[0, 'x', 0, 1, 1, 1, 1], 'C']), ('reset asserted in first cycle', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 1], [1, 0], [1, 0], [0, 0]]], [[0, 0, 0, 1], 'A']), ('start in accepting state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'C', [[1, 0], [1, 0], [1, 0], [1, 0], [1, 0], [0, 0], [1, 0]]], [[1, 1, 1, 1, 1, 1, 0], 'B'])]]
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
detects two ones[[0, 0, 1, 0, 0], 'A'][[0, 0, 1, 0, 0], 'A']Passed
reset while in output state[[0, 0, 1, 0, 0], 'C'][[0, 0, 1, 0, 0], 'C']Passed
missing transition holds state[[0, 0, 1, 0], 'A'][[0, 0, 1, 1], 'A']Failed
unknown input poisons state[[0, 0, 'x', 'x', 'x', 0], 'B'][[0, 0, 'x', 'x', 'x', 0], 'B']Passed
reset from unknown state[[0, 'x', 0], 'C'][[0, 'x', 0], 'C']Passed
reset asserted in first cycle[[0, 0, 0, 1], 'A'][[0, 0, 0, 1], 'A']Passed
start in accepting state[[1, 1, 0], 'B'][[1, 1, 0], 'B']Passed

SHA-256 / 3e4db4e51fef1aee362d81125216f2bdbec1944aecd6a84492e97151be6479a7

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(*args):
    table, start, stream = args
    state = start
    outs = []
    for bit, rst in stream:
        o = 'x' if state == 'X' else table[state]['out']
        if rst == 1:
            state = start
        elif state == 'X' or bit == 'x':
            state = 'X'
        else:
            state = table[state]['next'][str(bit)] if str(bit) in table[state]['next'] else 'X'
        outs.append(o)
    return [outs, state]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('detects two ones', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [0, 0], [1, 0], [0, 0]]], [[0, 0, 1, 0, 0], 'A']), ('reset while in output state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [1, 1], [1, 0], [1, 0]]], [[0, 0, 1, 0, 0], 'C']), ('missing transition holds state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [1, 0], [0, 0]]], [[0, 0, 1, 1], 'A']), ('unknown input poisons state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], ['x', 0], [1, 0], [0, 0], [0, 1], [1, 0]]], [[0, 0, 'x', 'x', 'x', 0], 'B']), ('reset from unknown state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'B', [['x', 0], [0, 1], [1, 0]]], [[0, 'x', 0], 'C']), ('reset asserted in first cycle', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 1], [1, 0], [1, 0], [0, 0]]], [[0, 0, 0, 1], 'A']), ('start in accepting state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'C', [[1, 0], [0, 0], [1, 0]]], [[1, 1, 0], 'B'])], [('detects two ones', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [0, 0], [1, 0], [0, 0], [0, 0]]], [[0, 0, 1, 0, 0, 0], 'A']), ('reset while in output state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [1, 1], [1, 0], [1, 0], [1, 0]]], [[0, 0, 1, 0, 0, 1], 'C']), ('missing transition holds state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [1, 0], [1, 0], [0, 0]]], [[0, 0, 1, 1, 1], 'A']), ('unknown input poisons state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], ['x', 0], [1, 0], [0, 0], [0, 0], [0, 1], [1, 0]]], [[0, 0, 'x', 'x', 'x', 'x', 0], 'B']), ('reset from unknown state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'B', [['x', 0], [0, 1], [1, 0], [1, 0]]], [[0, 'x', 0, 1], 'C']), ('reset asserted in first cycle', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 1], [1, 0], [1, 0]]], [[0, 0, 0], 'C']), ('start in accepting state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'C', [[1, 0], [1, 0], [0, 0], [1, 0]]], [[1, 1, 1, 0], 'B'])], [('detects two ones', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [0, 0], [1, 0], [0, 0], [0, 0], [0, 0]]], [[0, 0, 1, 0, 0, 0, 0], 'A']), ('reset while in output state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [1, 1], [1, 0], [1, 0], [1, 0], [1, 0]]], [[0, 0, 1, 0, 0, 1, 1], 'C']), ('missing transition holds state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [1, 0], [1, 0], [1, 0], [0, 0]]], [[0, 0, 1, 1, 1, 1], 'A']), ('unknown input poisons state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], ['x', 0], [1, 0], [0, 0], [0, 0], [0, 0], [0, 1], [1, 0]]], [[0, 0, 'x', 'x', 'x', 'x', 'x', 0], 'B']), ('reset from unknown state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'B', [['x', 0], [0, 1], [1, 0], [1, 0], [1, 0]]], [[0, 'x', 0, 1, 1], 'C']), ('reset asserted in first cycle', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 1], [1, 0], [1, 0], [0, 0]]], [[0, 0, 0, 1], 'A']), ('start in accepting state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'C', [[1, 0], [1, 0], [1, 0], [0, 0], [1, 0]]], [[1, 1, 1, 1, 0], 'B'])], [('detects two ones', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [0, 0], [1, 0], [0, 0], [0, 0], [0, 0], [0, 0]]], [[0, 0, 1, 0, 0, 0, 0, 0], 'A']), ('reset while in output state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [1, 1], [1, 0], [1, 0], [1, 0], [1, 0], [1, 0]]], [[0, 0, 1, 0, 0, 1, 1, 1], 'C']), ('missing transition holds state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [1, 0], [1, 0], [1, 0], [1, 0], [0, 0]]], [[0, 0, 1, 1, 1, 1, 1], 'A']), ('unknown input poisons state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], ['x', 0], [1, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 1], [1, 0]]], [[0, 0, 'x', 'x', 'x', 'x', 'x', 'x', 0], 'B']), ('reset from unknown state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'B', [['x', 0], [0, 1], [1, 0], [1, 0], [1, 0], [1, 0]]], [[0, 'x', 0, 1, 1, 1], 'C']), ('reset asserted in first cycle', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 1], [1, 0], [1, 0]]], [[0, 0, 0], 'C']), ('start in accepting state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'C', [[1, 0], [1, 0], [1, 0], [1, 0], [0, 0], [1, 0]]], [[1, 1, 1, 1, 1, 0], 'B'])], [('detects two ones', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [0, 0], [1, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0]]], [[0, 0, 1, 0, 0, 0, 0, 0, 0], 'A']), ('reset while in output state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [1, 1], [1, 0], [1, 0], [1, 0], [1, 0], [1, 0], [1, 0]]], [[0, 0, 1, 0, 0, 1, 1, 1, 1], 'C']), ('missing transition holds state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], [1, 0], [1, 0], [1, 0], [1, 0], [1, 0], [1, 0], [0, 0]]], [[0, 0, 1, 1, 1, 1, 1, 1], 'A']), ('unknown input poisons state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 0], ['x', 0], [1, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 1], [1, 0]]], [[0, 0, 'x', 'x', 'x', 'x', 'x', 'x', 'x', 0], 'B']), ('reset from unknown state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'B', [['x', 0], [0, 1], [1, 0], [1, 0], [1, 0], [1, 0], [1, 0]]], [[0, 'x', 0, 1, 1, 1, 1], 'C']), ('reset asserted in first cycle', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'A', [[1, 1], [1, 0], [1, 0], [0, 0]]], [[0, 0, 0, 1], 'A']), ('start in accepting state', [{'A': {'out': 0, 'next': {'1': 'B'}}, 'B': {'out': 0, 'next': {'0': 'A', '1': 'C'}}, 'C': {'out': 1, 'next': {'0': 'A'}}}, 'C', [[1, 0], [1, 0], [1, 0], [1, 0], [1, 0], [0, 0], [1, 0]]], [[1, 1, 1, 1, 1, 1, 0], 'B'])]]
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
detects two ones[[0, 0, 1, 0, 0], 'A'][[0, 0, 1, 0, 0], 'A']Passed
reset while in output state[[0, 0, 1, 0, 0], 'C'][[0, 0, 1, 0, 0], 'C']Passed
missing transition holds state[[0, 0, 1, 'x'], 'X'][[0, 0, 1, 1], 'A']Failed
unknown input poisons state[[0, 0, 'x', 'x', 'x', 0], 'B'][[0, 0, 'x', 'x', 'x', 0], 'B']Passed
reset from unknown state[[0, 'x', 0], 'C'][[0, 'x', 0], 'C']Passed
reset asserted in first cycle[[0, 0, 0, 1], 'A'][[0, 0, 0, 1], 'A']Passed
start in accepting state[[1, 'x', 'x'], 'X'][[1, 1, 0], 'B']Failed

SHA-256 / 5d8c5359c3d01a6c09a11ce77038737a97632837eae305cf9986780982d03fe1

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 7 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 deterministic bounded teaching model of one simulator rule set; the contract is stipulated and is not a claim of conformance to any HDL standard or commercial simulator. 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 2026-09-29T14:51:14.259945+00:00.

Case digest / b4c15adc621a3fb40f5fe5031bf8fb48d66df7703f0e83ec668d94b07fc7867e