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ITM · Recursively enumerable

Marching right forever

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

Never halts, and never repeats a configuration either: every 4 steps it is back in the same state with the same tape behind it, two cells further right. Proof: a translated cycler.

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ABChalt
The machine as drawn — 4 states, 6 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: the run repeats, shifted along fresh tape (a translated cycler), period 4.

Standard format1RB1RA_1RC1RZ_0LA0LCView on bbchallenge.org ↗

Notes

Standard format: 1RB1RA_1RC1RZ_0LA0LC