[Solved]: Bridge theorems for group theory and formal languages

Problem Detail: 

Is there some natural or notable way to relate or link math groups and CS formal languages or some other core CS concept e.g. Turing machines?

I am looking for references/applications. However note that I am aware of the link between semigroups and CS languages (namely via finite automata). (Does this literature on semiautomata ever look at "group-automata"?)

I have seen one paper many years ago that might come close, that converts TM transition tables into a binary operation, possibly sometimes a group in some cases, conceivably based on some kind of symmetry in the TM state table. It didn't explore that in particular, but also didn't rule it out.

Also, in particular, regarding the large body of math research on classification of finite groups, does or could it have any meaning or interpretation in TCS? What is the "algorithmic lens" view of this massive edifice of mathematical research? What is it "saying" about a possible hidden structure in computation?

This question is partly inspired by some other notes e.g.:

• Use of algebraic structures in TCS

• RJ Lipton on Gromov's theorem

Asked By : vzn

Answered By : J.-E. Pin

Let me first answer your subquestion: Does the literature on semiautomata ever look at "group-automata"?. The answer is yes. In his book (Automata, languages, and machines. Vol. B, Academic Press), S. Eilenberg gave a characterization of the regular languages recognized by finite commutative groups and $p$-groups. Similar results are known for finite nilpotent groups, soluble groups and supersoluble groups.

Finite groups also play an important role in the problem of finding a complete set of identities for regular expressions. An infinite complete set was proposed by John Conway and this conjecture was ultimately proved by D. Krob. There is a finite number of "basic" identities, plus an identity for each finite simple group. See my answer to this question for references.

In the opposite direction, finite automata theory lead to an elementary proof of basic results on combinatorial group theory, like the Schreier formula. Based on Stallings's seminal paper Topology of Finite Graphs.

Also in the opposite direction, automatic groups are defined in terms of finite automata.

Profinite groups also play an important role in automata theory. An example is the characterization of the regular languages recognized by transition-reversible automata with possibly several initial and final states.

For a very nice connection between context-free languages, groups and logic, see the article by David E. Muller and Paul E. Schupp, Context-free languages, groups, the theory of ends, second-order logic, tiling problems, cellular automata, and vector addition systems.

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Question Source : http://cs.stackexchange.com/questions/14398