27 research outputs found
Finite transducers for divisibility monoids
Divisibility monoids are a natural lattice-theoretical generalization of
Mazurkiewicz trace monoids, namely monoids in which the distributivity of the
involved divisibility lattices is kept as an hypothesis, but the relations
between the generators are not supposed to necessarily be commutations. Here,
we show that every divisibility monoid admits an explicit finite transducer
which allows to compute normal forms in quadratic time. In addition, we prove
that every divisibility monoid is biautomatic.Comment: 20 page
Set-theoretic solutions of the Yang-Baxter equation, RC-calculus, and Garside germs
Building on a result by W. Rump, we show how to exploit the right-cyclic law
(x.y).(x.z) = (y.x).(y.z) in order to investigate the structure groups and
monoids attached with (involutive nondegenerate) set-theoretic solutions of the
Yang-Baxter equation. We develop a sort of right-cyclic calculus, and use it to
obtain short proofs for the existence both of the Garside structure and of the
I-structure of such groups. We describe finite quotients that exactly play for
the considered groups the role that Coxeter groups play for Artin-Tits groups
Left-Garside categories, self-distributivity, and braids
In connection with the emerging theory of Garside categories, we develop the
notions of a left-Garside category and of a locally left-Garside monoid. In
this framework, the connection between the self-distributivity law LD and
braids amounts to the result that a certain category associated with LD is a
left-Garside category, which projects onto the standard Garside category of
braids. This approach leads to a realistic program for establishing the
Embedding Conjecture of [Dehornoy, Braids and Self-distributivity, Birkhauser
(2000), Chap. IX]
Monoids of O-type, subword reversing, and ordered groups
We describe a simple scheme for constructing finitely generated monoids in
which left-divisibility is a linear ordering and for practically investigating
these monoids. The approach is based on subword reversing, a general method of
combinatorial group theory, and connected with Garside theory, here in a
non-Noetherian context. As an application we describe several families of
ordered groups whose space of left-invariant orderings has an isolated point,
including torus knot groups and some of their amalgamated products.Comment: updated version with new result
Conjugacy problem for braid groups and Garside groups
We present a new algorithm to solve the conjugacy problem in Artin braid
groups, which is faster than the one presented by Birman, Ko and Lee. This
algorithm can be applied not only to braid groups, but to all Garside groups
(which include finite type Artin groups and torus knot groups among others).Comment: New version, with substantial modifications. 21 pages, 2 figure
Homology of Gaussian groups
We describe new combinatorial methods for constructing an explicit free
resolution of Z by ZG-modules when G is a group of fractions of a monoid where
enough least common multiples exist (``locally Gaussian monoid''), and,
therefore, for computing the homology of G. Our constructions apply in
particular to all Artin groups of finite Coxeter type, so, as a corollary, they
give new ways of computing the homology of these groups
Multifraction reduction I: The 3-Ore case and Artin-Tits groups of type FC
We describe a new approach to the Word Problem for Artin-Tits groups and,
more generally, for the enveloping group U(M) of a monoid M in which any two
elements admit a greatest common divisor. The method relies on a rewrite system
R(M) that extends free reduction for free groups. Here we show that, if M
satisfies what we call the 3-Ore condition about common multiples, what
corresponds to type FC in the case of Artin-Tits monoids, then the system R(M)
is convergent. Under this assumption, we obtain a unique representation result
for the elements of U(M), extending Ore's theorem for groups of fractions and
leading to a solution of the Word Problem of a new type. We also show that
there exist universal shapes for the van Kampen diagrams of the words
representing 1.Comment: 29 pages ; v2 : cross-references updated ; v3 : typos corrected;
final version due to appear in Journal of Combinatorial Algebr
Multifraction reduction II: Conjectures for Artin-Tits groups
Multifraction reduction is a new approach to the word problem for Artin-Tits
groups and, more generally, for the enveloping group of a monoid in which any
two elements admit a greatest common divisor. This approach is based on a
rewrite system ("reduction") that extends free group reduction. In this paper,
we show that assuming that reduction satisfies a weak form of convergence
called semi-convergence is sufficient for solving the word problem for the
enveloping group, and we connect semi-convergence with other conditions
involving reduction. We conjecture that these properties are valid for all
Artin-Tits monoids, and provide partial results and numerical evidence
supporting such conjectures.Comment: 41 pages , v2 : cross-references updated , v3 : exposition improved,
typos corrected, final version due tu appear in Journal of Combinatorial
Algebr