Library

ITM · Recursively enumerable

A halt nothing leads to

@thethinkmachine·version 1·CC BY 4.0·added 28 Sept 2026

State B has no move for a 1, so reading one would stop it. Searching backwards from that configuration shows nothing it can ever reach leads there. Proof: backward reasoning.

Open in AutomataStudio
More
Open in the desktop app Download the .automaton file Source on GitHub
ABC
The machine as drawn — 3 states, 5 transitions.

Behaviour

The first steps from a blank tape: one row per step, time running down; the outlined cell is the head.

Never halts from a blank tape. Proven: backward reasoning — no halting configuration is reachable.

Standard format1LB0RC_0RA---_1LB0LAView on bbchallenge.org ↗

Notes

Standard format: 1LB0RC_0RA---_1LB0LA