1RB3RB1LB---2RB 2LA1RA4LB2LA2RA

https://bbchallenge.org/1RB3RB1LB---2RB_2LA1RA4LB2LA2RA is a 2-state 5-symbol machine whose behavior is suspected to be similar to Skelet 17.

Analysis shared by Daniel Yuan (@dyuan01) on Discord, on June 14th 2024:

I just checked whenever the beaver reaches the 1 on the left side, and calculated the tape for when it next reaches the left side. It would be nice if someone can verify these rules.

[x, y, z] := 1 <B 4^x 12 4^y 12 4^z

[0, a, b, …] -> [a+3, b, …]
[2n+1, 2a, 2b, …, 0] -> Halt 
[2n+1, 2a, 2b, …, 2m+2] -> [2n, 2a, 2b, …, 2m+2, 0]
[2n+1, 2a, 2b, …, 2m+1] -> [2n, 2a, 2b, …, 2m+1, 1]
[2n+1, 2a, 2b, …, 2m+1, x, …] -> [2n, 2a, 2b, …, 2m+1, x+1, …]
[2n+2, a, b, …] -> [2n+1, a+1, b, …]

And you should start at [1, 1]