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ITM · Recursively enumerable

BB(2) champion

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

The two-state, two-symbol busy beaver: 6 steps, 4 ones. The largest number of steps any halting 2-state machine takes on a blank tape.

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ABhalt
The machine as drawn — 3 states, 4 transitions.

Behaviour

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

Halts from a blank tape after 6 steps, leaving 4 non-blank cells.

Standard format1RB1LB_1LA1RZView on bbchallenge.org ↗

Notes

Standard format: 1RB1LB_1LA1RZ