Finitely generated subgroups of free groups as formal languages and their cogrowth
For finitely generated subgroups $H$ of a free group $F_m$ of finite rank $m$, we study the language $L_H$ of reduced words that represent $H$ which is a regular language. Using the (extended) core of Schreier graph of $H$, we construct the minimal deterministic finite automaton that recognizes $L_H...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Episciences
2021-11-01
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| Series: | Groups, Complexity, Cryptology |
| Subjects: | |
| Online Access: | https://gcc.episciences.org/7617/pdf |
| Summary: | For finitely generated subgroups $H$ of a free group $F_m$ of finite rank
$m$, we study the language $L_H$ of reduced words that represent $H$ which is a
regular language. Using the (extended) core of Schreier graph of $H$, we
construct the minimal deterministic finite automaton that recognizes $L_H$.
Then we characterize the f.g. subgroups $H$ for which $L_H$ is irreducible and
for such groups explicitly construct ergodic automaton that recognizes $L_H$.
This construction gives us an efficient way to compute the cogrowth series
$L_H(z)$ of $H$ and entropy of $L_H$. Several examples illustrate the method
and a comparison is made with the method of calculation of $L_H(z)$ based on
the use of Nielsen system of generators of $H$. |
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| ISSN: | 1869-6104 |