Blue bilby refers to the small class of Turing machines up to 6 rules, i.e. machines with 2 states and 2 symbols, 3 states and 2 symbols or 2 states and 3 symbols.[1] 3 states and 2 symbols busy beaver is equal to 6. The name was given by James Harland[2] as part of his Zany Zoo project.[3]

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