Holdouts lists: Difference between revisions
→Busy Beaver for Lambda Calculus: added two more BBλ(37) holdouts lists |
→Busy Beaver adjacent holdouts lists: began adding fractran lists |
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|[https://discord.com/channels/960643023006490684/1239205785913790465/1400253700986900692 BBrev6_holdouts_409.txt] | |[https://discord.com/channels/960643023006490684/1239205785913790465/1400253700986900692 BBrev6_holdouts_409.txt] | ||
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=== Fractran === | |||
{| class="wikitable sortable" | |||
|+ | |||
!Domain | |||
!Date | |||
!Shared by | |||
!Number of holdouts | |||
!File | |||
!Notes | |||
|- | |||
|BBf(21) | |||
|[https://discord.com/channels/960643023006490684/1438019511155691521/1439725735211303003 November 16, 2025] | |||
|@dyuan01 | |||
|783 | |||
|[https://discord.com/channels/960643023006490684/1438019511155691521/1439725735211303003 message.txt] | |||
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|- | |||
|BBf(20) | |||
|[https://discord.com/channels/960643023006490684/1438019511155691521/1438483146864590900 November 13, 2025] | |||
|@-d | |||
|902 | |||
|[https://discord.com/channels/960643023006490684/1438019511155691521/1438483146864590900 sz20_902.txt] | |||
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|} | |} | ||
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|92 | |92 | ||
|[https://docs.google.com/spreadsheets/d/1yoiez7lDjZ-vRzj8NFWKWOxGlkK9IE_KWMUjeSWYWkw/edit?gid=0#gid=0 BBλ(37) 92 holdouts progress] | |[https://docs.google.com/spreadsheets/d/1yoiez7lDjZ-vRzj8NFWKWOxGlkK9IE_KWMUjeSWYWkw/edit?gid=0#gid=0 BBλ(37) 92 holdouts progress] | ||
| | |BBλ(37) has since been solved | ||
|- | |- | ||
|BBλ(37) | |BBλ(37) | ||
Revision as of 18:32, 28 March 2026
A holdout (or undecided machine) is a Turing machine for which it is not known whether the machine halts or not from an all-0 input tape. Holdouts are the machines which deciders are yet unable to decide. Contributors have shared lists of holdouts. Some lists exclude known equivalent machines, i.e., machines whose halting status is implied by the halting status of another machine. If a holdout machine with more than one undefined transitions is found to reach a undefined transition, the number of holdouts may increase as a consequence of TNF enumeration.
| 2-state | 3-state | 4-state | 5-state | 6-state | 7-state | |
|---|---|---|---|---|---|---|
| 2-symbol | 0 | 0 | 0 | 0 | 1161 | 18,036,852 |
| 3-symbol | 0 | 4 | 9,401,447 | |||
| 4-symbol | 0 | 12,435,284 | ||||
| 5-symbol | 69 | |||||
| 6-symbol | 548,993 |
Downloadable Holdouts Lists
This is a table where people have added lists with no restriction or independent verification. For some of the entries there is a reference to a spreadsheet that documents what was run to achieve the result. For others, there is additional documentation on the specific BB pages.
Busy Beaver adjacent holdouts lists
Beeping Busy Beaver
| Domain | Date | Shared by | Number of holdouts | File | Notes |
|---|---|---|---|---|---|
| BBB(4) | June 26, 2025 | @mxdys | 3713 | BBB4_holdouts_3713.txt |
Reversible Turing machines
| Domain | Date | Shared by | Number of holdouts | File | Notes |
|---|---|---|---|---|---|
| BBrev(6) | July 31, 2025 | @Sligocki | 388 | BBrev6_holdouts_388.txt | |
| BBrev(6) | July 31, 2025 | @Sligocki | 409 | BBrev6_holdouts_409.txt |
Fractran
| Domain | Date | Shared by | Number of holdouts | File | Notes |
|---|---|---|---|---|---|
| BBf(21) | November 16, 2025 | @dyuan01 | 783 | message.txt | |
| BBf(20) | November 13, 2025 | @-d | 902 | sz20_902.txt |
Terminating Turmites
| Domain | Date | Shared by | Number of holdouts | File | Notes |
|---|---|---|---|---|---|
| TT(2,4) | August 1, 2025 | @creeperman7002 | 2298 | holdout_2x4_2298.txt | |
| TT(4) | July 12, 2025 | @creeperman7002 | 99 | holdout4x2.txt |
Busy Beaver for Lambda Calculus
| Domain | Date | Shared by | Number of holdouts | File | Notes |
|---|---|---|---|---|---|
| BBλ(37) | March 27, 2025 | @Racheline | 92 | BBλ(37) 92 holdouts progress | BBλ(37) has since been solved |
| BBλ(37) | March 26, 2025 | @Racheline | 216 | BBL(37)_216.txt | |
| BBλ(37) | March 26, 2025 | @Racheline | 278 | BBL2(37)_278.txt | |
| BBλ(37) | March 26, 2025 | @Sam | 317 | BBL2(37)_317.txt | |
| BBλ(37) | March 26, 2025 | @Sam | 333 | BBL(37).txt |