16 research outputs found
Subexponential estimations in Shirshov's height theorem (in English)
In 1993 E. I. Zelmanov asked the following question in Dniester Notebook:
"Suppose that F_{2, m} is a 2-generated associative ring with the identity
x^m=0. Is it true, that the nilpotency degree of F_{2, m} has exponential
growth?" We show that the nilpotency degree of l-generated associative algebra
with the identity x^d=0 is smaller than Psi(d,d,l), where Psi(n,d,l)=2^{18} l
(nd)^{3 log_3 (nd)+13}d^2. We give the definitive answer to E. I. Zelmanov by
this result. It is the consequence of one fact, which is based on combinatorics
of words. Let l, n and d>n be positive integers. Then all the words over
alphabet of cardinality l which length is greater than Psi(n,d,l) are either
n-divided or contain d-th power of subword, where a word W is n-divided, if it
can be represented in the following form W=W_0 W_1...W_n such that W_1 >'
W_2>'...>'W_n. The symbol >' means lexicographical order here. A. I. Shirshov
proved that the set of non n-divided words over alphabet of cardinality l has
bounded height h over the set Y consisting of all the words of degree <n.
Original Shirshov's estimation was just recursive, in 1982 double exponent was
obtained by A.G.Kolotov and in 1993 A.Ya.Belov obtained exponential estimation.
We show, that h<Phi(n,l), where Phi(n,l) = 2^{87} n^{12 log_3 n + 48} l. Our
proof uses Latyshev idea of Dilworth theorem application.Comment: 21 pages, Russian version of the article is located at the link
arXiv:1101.4909; Sbornik: Mathematics, 203:4 (2012), 534 -- 55
Lyndon-Shirshov basis and anti-commutative algebras
Chen, Fox, Lyndon 1958 \cite{CFL58} and Shirshov 1958 \cite{Sh58} introduced
non-associative Lyndon-Shirshov words and proved that they form a linear basis
of a free Lie algebra, independently. In this paper we give another approach to
definition of Lyndon-Shirshov basis, i.e., we find an anti-commutative
Gr\"{o}bner-Shirshov basis of a free Lie algebra such that is the
set of all non-associative Lyndon-Shirshov words, where is the set of
all monomials of , a basis of the free anti-commutative algebra on ,
not containing maximal monomials of polynomials from . Following from
Shirshov's anti-commutative Gr\"{o}bner-Shirshov bases theory \cite{S62a2}, the
set is a linear basis of a free Lie algebra
The universal enveloping algebra of the Witt algebra is not noetherian
This work is prompted by the long standing question of whether it is possible
for the universal enveloping algebra of an infinite dimensional Lie algebra to
be noetherian. To address this problem, we answer a 23-year-old question of
Carolyn Dean and Lance Small; namely, we prove that the universal enveloping
algebra of the Witt (or centerless Virasoro) algebra is not noetherian. To show
this, we prove our main result: the universal enveloping algebra of the
positive part of the Witt algebra is not noetherian. We employ
algebro-geometric techniques from the first author's classification of
(noncommutative) birationally commutative projective surfaces.
As a consequence of our main result, we also show that the enveloping
algebras of many other infinite dimensional Lie algebras are not noetherian.
These Lie algebras include the Virasoro algebra and all infinite dimensional
Z-graded simple Lie algebras of polynomial growth
On finite complete rewriting systems, finite derivation type, and automaticity for homogeneous monoids
This paper investigates the class of finitely presented monoids defined by homogeneous (length-preserving) relations from a computational perspective. The properties of admitting a finite complete rewriting system, having finite derivation type, being automatic, and being biautomatic are investigated for this class of monoids. The first main result shows that for any consistent combination of these properties and their negations, there is a homogeneous monoid with exactly this combination of properties. We then introduce the new concept of abstract Rees-commensurability (an analogue of the notion of abstract commensurability for groups) in order to extend this result to show that the same statement holds even if one restricts attention to the class of n-ary homogeneous monoids (where every side of every relation has fixed length n). We then introduce a new encoding technique that allows us to extend the result partially to the class of n-ary multihomogenous monoids
On finite complete rewriting systems, finite derivation type, and automaticity for homogeneous monoids
This paper investigates the class of finitely presented monoids defined by homogeneous (length-preserving) relations from a computational perspective. The properties of admitting a finite complete rewriting system, having finite derivation type, being automatic, and being biautomatic are investigated for this class of monoids. The first main result shows that for any consistent combination of these properties and their negations, there is a homogeneous monoid with exactly this combination of properties. We then introduce the new concept of abstract Rees-commensurability (an analogue of the notion of abstract commensurability for groups) in order to extend this result to show that the same statement holds even if one restricts attention to the class of n-ary homogeneous monoids (where every side of every relation has fixed length n). We then introduce a new encoding technique that allows us to extend the result partially to the class of n-ary multihomogenous monoids