1RB1RD1LC_2LB1RB1LC_1RZ1LA1LD_2RB2RA2RD
(bbch) is a pentational halting BB(4,3) TM. It was discovered in May 2024 by Pavel Kropitz as one of seven long running TMs and achieves a score of over
Let , where
Rule 21 becomes:
Rule 23 becomes:
Rule 24 becomes:
Rule 25 becomes:
Rule 26 becomes:
Rule 27 becomes:
Rule 28 becomes:
- D(1, 0, c) --> halt with score 4c + 18
Rule 29 becomes:
By repeating rule 21, a stronger rule can be constructed:
If a is greater than or equal to 3:
=
This rule can also be repeated, also note that and :
The TM starts in configuration D(2, 2, 1).
D(2, 2, 1) -->
f_1(n) = 2^(n+4)*3 - 5
Note that the times three means that this expression of of the form 3k - 5 which can be rewritten as 3(k-1)-2 which can again be rewritten as 3(k-2)+1.
Next, 3k+1 mod 3 = 1
So f_1(n) mod 3 = 1
Thus f_1^a(n) mod 3 = 1
f_2(a,b) = f_1^(2*f_2(a-1,b)+11)(1)
Note that f_1^(2*f_2(a-1,b)+11)(1) is also of the form f_1^a(n)
Thus f_2(a,b) mod 3 = 1
-->
e_1 mod 3 = 1; 2*1 + 8 = 10 --> 10 mod 3 = 1
-->
-->
2e_3 + 7
Modulus: 2 + 7 --> 9 mod 3 = 0
-->
-->
e_3 mod 3 = 1; 2*1+5 = 7 --> 7 mod 3 = 1
-->
--> halts with score .
This can be bounded by: