An interesting parsing problem arises from @savask’s bouncers code.

We try to match the format s(n) = u1 w1^n u2 w2^n ... uk wk^n S> being given s(0), s(1), s(2). Example from @savask:

For example, if we have
s0 = 101 S>
s1 = 110011 S>
s2 = 110100111 S>
then
s(n) = 1 10^n 0 1^n 1 S>
and the tape formula will be
1 (10) 0 (1) 1 S>.

This is currently solved using dynamic programming, but we explore if there is a more efficient algo.

First, idea was the following greedy algorithm by @savask:

if all strings start with one symbol, throw it away. If not, try finding a longest prefix w of s1 such that w w is a prefix of s2, and throw those away.

Unfortunately, this fails on examples like the following:

I wrote another implementation of savask’s algorithm, in Rust. Like all my other deciders, it generates certificates that then get checked by a verifier proven correct in Coq. Thus, the results are almost guaranteed correct. This should brings us closer to a Bouncers decider that meets the verifiability & reproducibility standards – I think only the section of the decider-correctness document is missing?

When ran on the 32632 undecided machines, it decides 29799 machines in about 10 seconds. This is the same 29799 as Tony’s decider, according to @UncombedCoconut’s data. If I am understanding savask’s comments correctly, this also agrees with their implementation – since it’s slower by a few orders of magnitude, and requires a different I/O format, I didn’t bother actually running it to confirm.

This is very impressive work, you are really pushing bbchallenge on the tracks of automatic proofs at a faster rate than what I could have imagined in my dreams!!

I am going to read your code in depth as well as starting to write about bouncers in parallel.

mei’s optimised Rust implementation, reproducing savask’s. This implementation outputs certificates that are verified using Coq, more details about this approach will be given in future versions of the write-up.

Tristan Stérin’s (cosmo’s) Rust implementation, reproducing savask’s and mei’s. This implementation follows the write-up to the letter, reproducing each concept and algorithm as presented here. It is less efficient than mei’s.

Many thanks to @TonyG for initially presenting the method and to all the contributors that have participated in the release: @Iijil, @savask, @meithecatte, @UncombedCoconut, Pascal Michel, @cosmo.