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J. C. Birget

Publications and source records attributed to J. C. Birget.

14 recordsLinked to original sources
arXiv2026

On the complexity of the word problem of the R. Thompson group V

We analyze the proof by Lehnert and Schweitzer that the word problem of the Thompson group V is co-context-free, and we show that this word problem is the complement of the cyclic closure of a union of reverse deterministic context-free languages. The same is true for any finitely generated subgroup of V. For certain finite generating sets, this word problem is the complement of the cyclic closure of the union of four deterministic context-free languages. Therefore the word problem of V has quadratic time-complexity on a deterministic multitape Turing machine, and belongs to logDCFL.

math.GR↗
arXiv2024

Some properties of Higman-Thompson monoids and digital circuits

We define various monoid versions of the R. Thompson group $V$, and prove connections with monoids of acyclic digital circuits. We show that the monoid $M_{2,1}$ (based on partial functions) is not embeddable into Thompson's monoid ${\sf tot}M_{2,1}$, but that ${\sf tot}M_{2,1}$ has a submonoid that maps homomorphically onto $M_{2,1}$. This leads to an efficient completion algorithm for partial functions and partial circuits. We show that the union of partial circuits with disjoint domains is an element of $M_{2,1}$, and conversely, every element of $M_{2,1}$ can be decomposed efficiently into a union of partial circuits with disjoint domains.

math.GR↗
arXiv2021

Evaluation problems for the Thompson group and the Brin-Thompson group, and their relation to the word problem

The Thompson group $V$, as well as the Brin-Thompson group $2V$, is finitely generated and can be defined as a monoid acting on bitstrings, respectively pairs of bitstrings. Therefore evaluation problems can be defined for $V$ and $2V$. We show that these evaluation problems reduce to the corresponding word problems, and that in general, these evaluation problems are actually equivalent to the word problems. The long-input version of the evaluation problem is deterministic context-free and reverse deterministic context-free for $V,$ and P-complete for $2V$.

math.GR↗
arXiv2020

A monoid version of the Brin-Higman-Thompson groups

We generalize the Brin-Higman-Thompson groups $n G_{k,1}$ to monoids $n M_{k,1}$, for $n \ge 1$ and $k \ge 2$, by replacing bijections by partial functions. The monoid $n M_{k,1}$ has $n G_{k,1}$ as its group of units, and is congruence-simple. Moreover, $n M_{k,1}$ is finitely generated, and for $n \ge 2$ its word problem is {\sf coNP}-complete. We also present new results about higher-dimensional joinless codes.

math.GR↗
arXiv2020

The word problem of the Brin-Higman-Thompson groups

We show that the word problem of the Brin-Higman-Thompson group $n G_{k,1}$ is {\sf coNP}-complete for all $n \ge 2$ and all $k \ge 2$. For this we prove that $n G_{k,1}$ is finitely generated, and that $n G_{k,1}$ contains a subgroup of $2 G_{2,1}$ that can represent bijective circuits. We also show that for all $n \ge 1$ and $k \ge 2$: \ If $\,K = 1 + (k-1)\,N\,$ for some $N \ge 1$, then $n G_{K,1} \le n G_{k,1}$. In particular, $n G_{K,1} \le n G_{2,1}$ for all $K \ge 2$.

math.GR↗
arXiv2020

The word problem of the Brin-Thompson group is coNP-complete

We prove that the word problem of the Brin-Thompson group nV over a finite generating set is coNP-complete for every n \ge 2. It is known that the groups nV are an infinite family of infinite, finitely presented, simple groups. We also prove that the word problem of the Thompson group V over a certain infinite set of generators, related to boolean circuits, is coNP-complete.

math.GR↗
arXiv2019

Global local covers

This paper gives a systematic construction of certain covers of finite semigroups. These covers will be used in future work on the complexity of finite semigroups.

math.GR↗
arXiv2019

New embeddings between the Higman-Thompson groups

We give a direct proof that all Higman-Thompson groups of the form $G_{k,1}$ (for $k \ge 2$) are embedded in one another, which is a recent result of N. Matte Bon. This extends the embeddings given by Higman in 1974.

math.GR↗
arXiv2018

Polynomial-time right-ideal morphisms and congruences

We continue with the functional approach to the P-versus-NP problem, begun in [2, 3]. We previously constructed a monoid RM^P that is non-regular iff NP is not P. We now construct homomorphic images of RM^P with interesting properties. In particular, the homomorphic image M^P_poly of RM^P is finitely generated and J^0-simple, and is non-regular iff NP is not P. The group of units of M^P_poly is the famous Richard Thompson group V.

math.GR↗
arXiv2017

Inverse monoids associated with the complexity class NP

We study the P versus NP problem through properties of functions and monoids, continuing the work of [3]. Here we consider inverse monoids whose properties and relationships determine whether P is different from NP, or whether injective one-way functions (with respect to worst-case complexity) exist.

math.GR↗
arXiv2016

Infinitely generated semigroups and polynomial complexity

This paper continues the functional approach to the P-versus-NP problem, begun in [1]. Here we focus on the monoid RM_2^P of right-ideal morphisms of the free monoid, that have polynomial input balance and polynomial time-complexity. We construct a machine model for the functions in RM_2^P, and evaluation functions. We prove that RM_2^P is not finitely generated, and use this to show separation results for time-complexity.

math.GR↗
arXiv2016

Monoid generalizations of the Richard Thompson groups

The groups G_{k,1} of Richard Thompson and Graham Higman can be generalized in a natural way to monoids, that we call M_{k,1}, and to inverse monoids, called Inv_{k,1}; this is done by simply generalizing bijections to partial functions or partial injective functions. The monoids M_{k,1} have connections with circuit complexity (studied in another paper). Here we prove that M_{k,1} and Inv_{k,1} are congruence-simple for all k. Their Green relations J and D are characterized: M_{k,1} and Inv_{k,1} are J-0-simple, and they have k-1 non-zero D-classes. They are submonoids of the multiplicative part of the Cuntz algebra O_k. They are finitely generated, and their word problem over any finite generating set is in P. Their word problem is coNP-complete over certain infinite generating sets. Changes in this version: Section 4 has been thoroughly revised, and errors have been corrected; however, the main results of Section 4 do not change. Sections 1, 2, and 3 are unchanged, except for the proof of Theorem 2.3, which was incomplete; a complete proof was published in the Appendix of reference [6], and is also given here.

math.GR↗
arXiv2015

Semigroups and one-way functions

We study the complexity classes P and NP through a semigroup fP ("polynomial-time functions"), consisting of all polynomially balanced polynomial-time computable partial functions. Then P is not equal to NP iff fP is a non-regular semigroup. The one-way functions considered here are based on worst-case complexity (they are not cryptographic); they are the non-regular elements of fP. We prove various properties of fP, e.g., that it is finitely generated. We define reductions with respect to which certain universal one-way functions are fP-complete.

math.GR↗