共查询到20条相似文献,搜索用时 500 毫秒
1.
We prove that finite flat digraph algebras and, more generally, finite compatible flat algebras satisfying a certain condition
are finitely q-based (possess a finite basis for their quasiequations). We also exhibit an example of a twelve-element compatible flat algebra
that is not finitely q-based.
The first author was partially supported by the grant # 201/02/0594 of the Grant Agency of the Czech Republic, and by the
Institutional grant MSM0021620839; the second author was partially supported by the grant No. Tn37877 of the Hungarian National
Foundation for Scientific Research (OTHA); the third author was supported by the NSF grant # DMS-9971352. 相似文献
2.
Miklós Maróti 《Algebra Universalis》2007,57(2):215-237
We investigate the near-unanimity problem: given a finite algebra, decide if it has a near-unanimity term of finite arity.
We prove that it is undecidable of a finite algebra if it has a partial near-unanimity term on its underlying set excluding
two fixed elements. On the other hand, based on Rosenberg’s characterization of maximal clones, we present partial results
towards proving the decidability of the general problem.
While working on this paper, the author was partially supported by the Hungarian National Foundation for Scientific Research
(OTKA) grant nos. T 37877 and K 60148. 相似文献
3.
A finite, nontrivial algebra is order-primal if its term functions are precisely the monotone functions for some order on the underlying set. We show that the prevariety generated by an order-primal algebra P is relatively congruence-distributive and that the variety generated by P is congruence-distributive if and only if it contains at most two non-ismorphic subdirectly irreducible algebras. We also prove that if the prevarieties generated by order-primal algebras P and Q are equivalent as categories, then the corresponding orders or their duals generate the same order variety. A large class of order-primal algebras is described each member of which generates a variety equivalent as a category to the variety determined by the six-element, bounded ordered set which is not a lattice. These results are proved by considering topological dualities with particular emphasis on the case where there is a monotone near-unanimity function.This research was carried out while the third author held a research fellowship at La Trobe University supported by ARGS grant B85154851. The second author was supported by a grant from the NSERC. 相似文献
4.
Ladislav Bican 《Czechoslovak Mathematical Journal》2008,58(2):561-568
In the class of all exact torsion theories the torsionfree classes are cover (pre-cover) classes if and only if the classes
of torsionfree relatively injective modules or relatively exact modules are cover (precover) classes, and this happens exactly
if and only if the torsion theory is of finite type. Using the transfinite induction in the second half of the paper a new
construction of a torsionfree relatively injective cover of an arbitrary module with respect to Goldie’s torsion theory of
finite type is presented.
This research has been partially supported by the Grant Agency of the Czech Republic, grant #GAČR 201/06/0510 and also by
the institutional grant MSM 0021620839. 相似文献
5.
We find all finite unavoidable ordered sets, finite unavoidable semilattices and finite unavoidable lattices.
While working on this paper, the second and third authors were supported by US NSF grant DMS-0604065. The second author was
also supported by the Grant Agency of the Czech Republic, grant #201/05/0002 and by the institutional grant MSM0021620839
financed by MSMT. 相似文献
6.
The polynomial functions of an algebra preserve all congruence relations. In addition, if the algebra is finite, they preserve
the labelling of the congruence lattice in the sense of Tame Congruence Theory. The question is for which algebras every congruence
preserving function, or at least every function that preserves the labelling of the congruence lattice, is a polynomial function.
In this paper, we investigate this question for finite algebras that have a group reduct.
Presented by K. Kaarli.
Received March 12, 2006; accepted in final form October 16, 2008.
The second author is supported by Grant No. 144011 of the Ministry of Science of the Republic of Serbia, and the Scholarship
“One-Month Visits to Austria for University Graduates” WUS-Austria, from the Austrian Ministry of Education, Science and Culture. 相似文献
7.
Let G be a locally compact group. We show that its Fourier algebra A(G) is amenable if and only if G has an abelian subgroup of finite index, and that its Fourier–Stieltjes algebra B(G) is amenable if and only if G has a compact, abelian subgroup of finite index. We then show that A(G) is weakly amenable if the component of the identity of G is abelian, and we prove some partial results towards the converse.Research supported by NSERC under grant no. 90749-00.Research supported by NSERC under grant no. 227043-00. 相似文献
8.
Let Λ be a finite dimensional algebra over a field k. We will show here that Λ is piecewise hereditary if and only if its strong global dimension is finite.
Dedicated to Otto Kerner on the occasion of his 65th birthday.
The second author is supported by a grant from NSA. These results were obtained during a visit of the first author at Syracuse
University. He would like to thank the second author for the hospitality during his stay. 相似文献
9.
Stephen D. Smith 《Geometriae Dedicata》1991,37(1):103-118
The notion of weight algebra for a group geometry is developed for flag-transitive subgroups and their quotients, as a technique
for establishing the existence of weight vectors in modular representations. This extends the applicability of earlier results,
in particular results for the full group of a spherical building. The method adapts for at least some of the sporadic geometries
provided by finite quotients of infinite affine buildings.
Dedicated to Professor Jacques Tits on his 60th birthday
Partially supported by NSF grant DMS 88-01679 and NSA grant MDA 904-87-H-2006. 相似文献
10.
An algebra is called weakly diagonal if every subuniverse of its square contains the graph of an automorphism. We show that
every variety generated by a finite algebra with no proper subalgebras has a weakly diagonal generator. The result is applied
in several ways and, in particular, to show that every arithmetical affine complete variety of finite type has equationally
definable principal congruences.
This paper is dedicated to Walter Taylor.
Received February 22, 2005; accepted in final form June 3, 2005.
Work of the first author was supported by grant No. 5368 from The Estonian Science
Foundation. 相似文献
11.
This paper gives a uniform, self-contained, and fairly direct approach to a variety of obstruction-theoretic problems on 8-manifolds.
We give necessary and sufficient cohomological criteria for the existence of complex and quaternionic structures on eight-dimensional
vector bundles and for the reduction of the structure group of such bundles to U(3) by the homomorphism U(3) → O(8) given
by the Lie algebra representation of PU(3).
Research of M. Čadek supported by the grant MSM 0021622409 of the Czech Ministry of Education. Research of J. Vanžura supported
by the Academy of Sciences of the Czech Republic, Institutional Research Plan AVOZ10190503, and by the grant 201/05/2117 of
the Grant Agency of the Czech Republic. 相似文献
12.
A finite algebra is said to be order-primal if its clone of all term operations is the set of all operations defined on A which preserve a given partial order ≤ on A. In this paper we study algebraic properties of order-primal algebras for connected ordered sets (A; ≤). Such order-primal algebras are constantive, simple and have no non-identical automorphisms. We show that in this case cannot have only unary fundamental operations or only one at least binary fundamental operation. We prove several properties of the varieties and the quasi-varieties generated by constantive and simple algebras and apply these properties to order-primal algebras. Further, we use the properties of order-primal algebras to formulate new primality criteria for finite algebras.* Research supported by the Hungarian research grant No. TO34137 and by the János Bolyai grant.** Research supported by the Thailand Research Fund. 相似文献
13.
The decision problem for provability logic remains PSPACE-complete even if the number of propositional atoms is restricted to one.
This paper was supported by grant 401/01/0218 of the Grant Agency of the Czech Republic. 相似文献
14.
Aleš Drápal 《Czechoslovak Mathematical Journal》2005,55(1):61-86
If Q is a quasigroup that is free in the class of all quasigroups which are isotopic to an Abelian group, then its multiplication group Mlt Q is a Frobenius group. Conversely, if Mlt Q is a Frobenius group, Q a quasigroup, then Q has to be isotopic to an Abelian group. If Q is, in addition, finite, then it must be a central quasigroup (a T-quasigroup).This work was supported by institutional grant MSM 113200007, and by Grant Agency of Czech Republic, grant number 201/99/0263. 相似文献
15.
Let be a finite-dimensional hereditary algebra of finite or tame representation type over a finite field, and let be a rigid -module. Then the element in the Ringel–Hall algebra is an iterated skew commutator of the isoclasses of simple -modules. This gives a new characterization of the rigidness of an indecomposable module over a tame hereditary algebra.The first author was partially supported by a grant from the NSF; and the second author was supported by the Doctorial Foundation of the Ministry of Education of People’s Republic of China, and the NSFC (Grant No. 10271113 and 10301033). 相似文献
16.
We study the exponential rate of growth of the sequence of proper, Lie and Jordan codimensions of an associative algebra.
We show that for any finite dimensional associative algebra, the exponential rates of growth can be explicitly computed and
are strictly related to the PI-exponent of the algebra.
The first author was partially supported by MIUR of Italy. The second author was partially supported by RFBR grant No 06-01-00485
and SSC-5666.2006.1 相似文献
17.
Petr Knobloch 《Applications of Mathematics》2006,51(5):473-493
It is well known that finite element spaces used for approximating the velocity and the pressure in an incompressible flow
problem have to be stable in the sense of the inf-sup condition of Babuška and Brezzi if a stabilization of the incompressibility
constraint is not applied. In this paper we consider a recently introduced class of triangular nonconforming finite elements
of nth order accuracy in the energy norm called P
n
mod
elements. For n ≤ 3 we show that the stability condition holds if the velocity space is constructed using the P
n
mod
elements and the pressure space consists of continuous piecewise polynomial functions of degree n.
This research has been supported by the Grant Agency of the Czech Republic under the grant No. 201/05/0005 and by the grant
MSM 0021620839. 相似文献
18.
We describe an explicit construction whicy, for some fixed absolute positive constant ε, produces, for every integers>1 and all sufficiently largem, a graph on at least
vertices containing neither a clique of sizes nor an independent set of sizem.
Part of this work was done at the Institute for Advanced Study, Princeton, NJ 08540, USA. Research supported in part by a
USA Israeli BSF grant, by a grant from the Israel Science Foundation and by the Hermann Minkowski Minerva Center for Geometry
at Tel Aviv University.
Research supported in part by a grant A1019901 of the Academy of Sciences of the Czech Republic and by a cooperative research
grant INT-9600919/ME-103 from the NSF (USA) and the MŠMT (Czech Republic). 相似文献
19.
Over the past fifty years, finite element methods for the approximation of solutions of partial differential equations (PDEs)
have become a powerful and reliable tool. Theoretically, these methods are not restricted to PDEs formulated on physical domains
up to dimension three. Although at present there does not seem to be a very high practical demand for finite element methods
that use higher dimensional simplicial partitions, there are some advantages in studying the methods independent of the dimension.
For instance, it provides additional insights into the structure and essence of proofs of results in one, two and three dimensions.
In this survey paper we review some recent progress in this direction.
The second author was supported by Grant No. 112444 of the Academy of Finland. The third author was supported by grant No.
201/04/1503 of the Grant Agency of the Czech Republic. 相似文献
20.
Let be the ordered set of isomorphism types of finite distributive lattices, where the ordering is by embeddability. We characterize
the order ideals in that are well-quasi-ordered by embeddability, and thus characterize the members of that belong to at least one infinite anti-chain in .
While working on this paper, the second and third authors were supported by US NSF grant DMS-0604065. The second author was
also supported by the Grant Agency of the Czech Republic, grant #201/05/0002 and by the institutional grant MSM0021620839
financed by MSMT. 相似文献