共查询到20条相似文献,搜索用时 10 毫秒
1.
2.
3.
On equalizer-flat and pullback-flat acts 总被引:4,自引:0,他引:4
Peeter Normak 《Semigroup Forum》1987,36(1):293-313
4.
Akbar Golchin 《Semigroup Forum》2003,67(2):262-270
We consider monoids $S=G\dot \cup I$ where G is a group and I is an ideal of S and show that if an S-act is principally weakly flat, (weakly) flat, torsion free or satisfies conditions (P) or (PE) as an I1-act, then it has these properties as an S-act. We also show that an S-act which is free, projective or strongly flat as an I1-act may not generally have these properties as an S-act. 相似文献
5.
The paper is devoted to the investigation of uniform acts over semigroups perceived as an overclass of subdirectly irreducible acts. We establish conditions for a uniform act to be subdirectly irreducible. In particular, we prove that uniform acts with two zeros are subdirectly irreducible. Ultimately we investigate monoids which are uniform as right acts over themselves and we describe regular monoids with this property. 相似文献
6.
7.
8.
In this article, we present an extension of the concept of weakly projective acts to the socalled (S/I, S/J)-projective acts. Retracts, coproducts, and products of acts as well as Rees factor acts are considered from the point of
view of these properties. They are used to describe monoids that are disjoint unions of a group with a left zero semigroup
or with a disjoint union of simple right ideals. We suggest concepts of weak QF-monoids.
__________
Translated from Fundamentalnaya i Prikladnaya Matematika, Vol. 10, No. 3, pp. 85–96, 2004. 相似文献
9.
Michael Krivelevich Benny Sudakov Prasad Tetali 《Random Structures and Algorithms》2006,29(2):180-193
We study a model of random graphs, where a random instance is obtained by adding random edges to a large graph of a given density. The research on this model has been started by Bohman and colleagues (Random Struct Algor 3 ; Random Struct Algor 4 ). Here we obtain a sharp threshold for the appearance of a fixed subgraph and for certain Ramsey properties. We also consider a related model of random k‐SAT formulas, where an instance is obtained by adding random k‐clauses to a fixed formula with a given number of clauses, and derive tight bounds for the non‐satisfiability of the thus‐obtained random formula. © 2006 Wiley Periodicals, Inc. Random Struct. Alg., 2006 相似文献
10.
On covers of cyclic acts over monoids 总被引:1,自引:0,他引:1
In (Bull. Lond. Math. Soc. 33:385–390, 2001) Bican, Bashir and Enochs finally solved a long standing conjecture in module theory that all modules over a unitary ring
have a flat cover. The only substantial work on covers of acts over monoids seems to be that of Isbell (Semigroup Forum 2:95–118,
1971), Fountain (Proc. Edinb. Math. Soc. (2) 20:87–93, 1976) and Kilp (Semigroup Forum 53:225–229, 1996) who only consider projective covers. To our knowledge the situation for flat covers of acts has not been addressed and this
paper is an attempt to initiate such a study. We consider almost exclusively covers of cyclic acts and restrict our attention
to strongly flat and condition (P) covers. We give a necessary and sufficient condition for the existence of such covers and for a monoid to have the property that
all its cyclic right acts have a strongly flat cover (resp. (P)-cover). We give numerous classes of monoids that satisfy these conditions and we also show that there are monoids that do
not satisfy this condition in the strongly flat case. We give a new necessary and sufficient condition for a cyclic act to
have a projective cover and provide a new proof of one of Isbell’s classic results concerning projective covers. We show also
that condition (P) covers are not unique, unlike the situation for projective covers. 相似文献
11.
Archiv der Mathematik - 相似文献
12.
D.P. Baturov 《Topology and its Applications》2007,154(2):374-383
Let M be a separable metric space consisting of more than one point. We construct perfectly normal dense subspaces Z⊂Mc2 and (under additional set-theoretic assumption) Y⊂Mc which are not collectionwise Hausdorff. 相似文献
13.
The tree-depth of is the smallest value of for which a labeling of the vertices of with elements from exists such that any path joining two vertices with the same label contains a vertex having a higher label. The graph is -critical if it has tree-depth and every proper minor of has smaller tree-depth.Motivated by a conjecture on the maximum degree of -critical graphs, we consider the property of 1-uniqueness, wherein any vertex of a critical graph can be the unique vertex receiving label 1 in an optimal labeling. Contrary to an earlier conjecture, we construct examples of critical graphs that are not 1-unique and show that 1-unique graphs can have arbitrarily many more edges than certain critical spanning subgraphs. We also show that -critical graphs on vertices are 1-unique and use 1-uniqueness to show that the Andrásfai graphs are critical with respect to tree-depth. 相似文献
14.
Communicated by J. Lawson 相似文献
15.
Summary The central problem of this paper is the question of denseness of those
planar point sets <InlineEquation ID=IE"1"><EquationSource Format="TEX"><![CDATA[<InlineEquation ID=IE"2"><EquationSource
Format="TEX"><![CDATA[<InlineEquation ID=IE"3"><EquationSource Format="TEX"><![CDATA[<InlineEquation ID=IE"4"><EquationSource
Format="TEX"><![CDATA[<InlineEquation ID=IE"5"><EquationSource Format="TEX"><![CDATA[$]]></EquationSource></InlineEquation>]]></EquationSource></InlineEquation>]]></EquationSource></InlineEquation>]]></EquationSource></InlineEquation>]]></EquationSource></InlineEquation>\mathcal{P}$,
not a subset of a line, which have the
property that for every three noncollinear points in $\mathcal{P}$, a specific
triangle center (incenter (IC), circumcenter (CC), orthocenter (OC) resp.) is
also in the set $\mathcal{P}$. The IC and CC versions were settled before.
First we generalize and solve the CC problem in higher dimensions. Then we
solve the OC problem in the plane essentially proving that $\mathcal{P}$ is
either a dense point set of the plane or it is a subset of a rectangular
hyperbola. In the latter case it is either a dense subset or it is a special
discrete subset of a rectangular hyperbola. 相似文献
16.
Zvi Artstein 《Rendiconti del Circolo Matematico di Palermo》1984,33(3):340-350
Representations of multivalued maps as pointwise closure of a sequence of point-valued functions are derived from functional analytic considerations. Characterizations of convergence in the space of multifunctions, and of the ensemble of selections are implied. 相似文献
17.
The notions of thin and very thin dense subsets of a product space were introduced by the third author, and in this article we also introduce the notion of a slim dense set in a product. We obtain a number of results concerning the existence and non-existence of these types of small dense sets, and we study the relations among them. 相似文献
18.
19.
K. Zh. Kudaĭbergenov 《Siberian Advances in Mathematics》2014,24(1):43-46
We obtain results on existence of dense free subgroups of the automorphism group of a homogeneous model. 相似文献
20.
Zhu Yaochen 《数学学报(英文版)》1989,5(4):329-336
In the present paper a form of generalization of Gelfond's lemma on dense sequences of polynomials is proposed. For a set of complex numbers
1, ...,
s
we define the coefficientsgk(
1, ...,
s
) (0ks) and give the relations between them and the transcendental degrees or the transcendence types of the field © (
1, ...,
s
) or its subfields.This work was completed at the Dept. of Math., Univ. of Southern Mississippi, USA in 1987. 相似文献