9 hours ago
- A holdout (or undecided machine) is a Turing machine whose halting status from an all-0 input tape is unknown, and deciders cannot yet decide it.
- Tables show the number of holdouts for different Busy Beaver spaces (e.g., 2-state, 3-symbol) and for various state/symbol combinations, with entries like 1064 for BB(6) 2-symbol and 11,362,197 for BB(3,4).
- A large table lists downloadable holdout files shared by contributors, with dates, numbers of holdouts, and notes on reductions, equivalences, and work done (e.g., by @mxdys, @Justin Blanchard, etc.).
- Holdout lists also exist for related problems such as Beeping Busy Beaver, Reversible Turing machines, and Busy Beaver for Lambda Calculus.