共查询到20条相似文献,搜索用时 150 毫秒
1.
Brunetto Piochi 《Semigroup Forum》1991,43(1):151-162
LetS be a semigroup;S is said to bepermutable if, for some integern, every product ofn elements ofS can be re-ordered. We prove that every normal extension of a semilattice by an inverse permutable semigroupsis permutable.
Also, some properties of permutable groups are extended to inverse semigroups. 相似文献
2.
James C. S. Wong 《Semigroup Forum》1986,35(1):227-236
LetS be a uniform semigroup (this includes all topological groups and affine semigroups). We show that a certain space of uniformly
continuous functions onS has a left invariant mean iffS has the fixed point property for uniformly continuous affine actions ofS on compact convex sets. This is closely related to but independent of the results of T. Mitchell in [13] and A. Lau in [10].
Interesting examples and consequences are given for the special cases of topological groups and affine convolution semigroups
of probability measures on a locally compact semigroup or group.
Research Supported by NSERC of Canada Grant No. A8227. 相似文献
3.
Hanson Umoh 《Semigroup Forum》1992,44(1):118-124
For α∈N with α≥2, we define and characterize α-inflatable semigroups,S and establish that the product (βS/S,·)·(βS/S,·) of Stone-Ĉech remainders does not contain the closure of the minimal ideal of (βS,·), the Stone-Ĉech compactification ofS. From this result, one can easily derive Ruppert's result that the minimal ideal of a compact left-topological semigroup
is not necessarily closed.
The author gratefully acknowledges support from Delaware State College under Grant No. 6769. 相似文献
4.
LetG be any compact non-commutative simple Lie group not locally isomorphic to SO(3). We present a generalization of a theorem
of Lubotzky, Phillips and Sarnak on distributing points on the sphere S2 (or S3) to any homogeneous space ofG, in particular, to all higher dimensional spheres. Our results can also be viewed as a quantitative solution to the generalized
Ruziewicz problem for any homogeneous space ofG.
Partially supported by DMS-0070544 and DMS-0333397. 相似文献
5.
We introduce two notions of amenability for a Banach algebra A. LetI be a closed two-sided ideal inA, we sayA is I-weakly amenable if the first cohomology group ofA with coefficients in the dual space I* is zero; i.e.,H
1(A, I*) = {0}, and,A is ideally amenable ifA isI-weakly amenable for every closed two-sided idealI inA. We relate these concepts to weak amenability of Banach algebras. We also show that ideal amenability is different from amenability
and weak amenability. We study theI-weak amenability of a Banach algebraA for some special closed two-sided idealI. 相似文献
6.
In this paper we study the ideal amenability of Banach algebras. LetA be a Banach algebra and letI be a closed two-sided ideal inA, A isI-weakly amenable ifH
1(A,I
*) = {0}. Further,A is ideally amenable ifA isI-weakly amenable for every closed two-sided idealI inA. We know that a continuous homomorphic image of an amenable Banach algebra is again amenable. We show that for ideal amenability
the homomorphism property for suitable direct summands is true similar to weak amenability and we apply this result for ideal
amenability of Banach algebras on locally compact groups. 相似文献
7.
Abdülkadir özdeğer 《Journal of Geometry》1999,64(1-2):150-159
LetS be a surface of classC
4 in 3-dimensional Euclidean space. In this paper it is shown that any two of the following three conditions imply the third one: (a)S is a minimal surface, (b) Two families of Laguerre lines ofS form a conjugate net, (c)S is a non-developable ruled surface. Furthermore, it is proved that any surface (other than a sphere, a cylinder of revolution and a plane) of constant mean curvature on which the two families of Laguerre lines form a conjugate net is a minimal-helicoid. 相似文献
8.
George Converse 《Israel Journal of Mathematics》1977,27(2):124-130
LetM be a point andS be a compact set inR
2 such thatS is the closure of its interior. The theorem desired says that ifM is a mode ofS thenS is convex and centrally symmetric with respect toM. Some conditions on the boundary ofS are needed for the proof given. 相似文献
9.
LetS be a compact orientable surface, letQ be the moduli space of quadratic differentials onS and letM be a stratum inQ. We explicitly describe the minimal sets for the (Teichmüller) horocycle flow onM and onQ, and show that these correspond to horizontal cylindrical decompositions ofS. 相似文献
10.
Matatyahu Rubin 《Israel Journal of Mathematics》1974,17(4):392-443
LetT be a complete theory of linear order; the language ofT may contain a finite or a countable set of unary predicates. We prove the following results. (i) The number of nonisomorphic
countable models ofT is either finite or 2ω. (ii) If the language ofT is finite then the number of nonisomorphic countable models ofT is either 1 or 2ω. (iii) IfS
1(T) is countable then so isS
n(T) for everyn. (iv) In caseS
1(T) is countable we find a relation between the Cantor Bendixon rank ofS
1(T) and the Cantor Bendixon rank ofS
n(T). (v) We define a class of modelsL, and show thatS
1(T) is finite iff the models ofT belong toL. We conclude that ifS
1(T) is finite thenT is finitely axiomatizable. (vi) We prove some theorems concerning the existence and the structure of saturated models.
Most of the results in this paper appeared in the author’s Master of Science thesis which was prepared at the Hebrew University
under the supervision of Professor H. Gaifman. 相似文献
11.
LetS be a semigroup andE the set of all idempotents inS. LetS-Act be the category of allS-acts. LetC be a full subcategory ofS-Act which containss
S and is closed under coproducts and summands. It is proved that, inC, anS-actP is projective and unitary if and only ifP≅ ∐
jϕ
I
Se
i
,e
i
ϕE. In particular,P is a projective, indecomposable and unitary object if and only ifP ≅Se for somee ∈E. These generalize some results obtained by Knauer and Talwar.
Research partially supported by a UGC (HK) (Grant No. 2160092). 相似文献
12.
Herve Loïc 《Integral Equations and Operator Theory》1998,32(2):199-215
LetX be a locally compact space, andT, a quasi-compact positive operator onC
0(X), with positive spectral radius,r. Then the peripheral spectrum ofT is a finite set of poles containingr, and the residue of the resolvent ofT at each peripheral pole is of finite rank. Using the concept of closed absorbing set, we develop an iterative process that gives the order,p, ofr, some special bases of the algebraic eigenspaces ker(T-r)
p
and ker(T
*-r)
p
, and finally the dimension of the algebraic eigenspace associated to each peripheral pole. 相似文献
13.
We introduce the notion of semigroup with a tight ideal series and investigate their closures in semitopological semigroups,
particularly inverse semigroups with continuous inversion. As a corollary we show that the symmetric inverse semigroup of
finite transformations I
λ
n
of the rank ≤
n is algebraically closed in the class of (semi)topological inverse semigroups with continuous inversion. We also derive related
results about the nonexistence of (partial) compactifications of classes of semigroups that we consider. 相似文献
14.
LetS be a semigroup andE the set of all idempotents inS. LetS-Act be the category of allS-acts. LetC be a full subcategory ofS-Act which containss
S and is closed under coproducts and summands. It is proved that, inC, anS-actP is projective and unitary if and only ifP≅ ∐
jϕ
I
Se
i
,e
i
ϕE. In particular,P is a projective, indecomposable and unitary object if and only ifP ≅Se for somee ∈E. These generalize some results obtained by Knauer and Talwar. 相似文献
15.
LetG be a finite transitive permutation group on a finite setS. LetA be a nonempty subset ofS and denote the pointwise stabilizer ofA inG byC
G
(A). Our main result is the following inequality: [G :C
G
(A)]≥|G||A|/|S|.
This paper is a part of the author’s Ph.D. thesis research, carried out at Tel Aviv University under the supervision of Professor
Marcel Herzog. 相似文献
16.
Guangtian Song 《Semigroup Forum》1995,51(1):295-298
LetR be a ring with identity,S be a semigroup with the set of idempotentsE(S), and denote (E(S)) for the subsemigroup ofS generated byE(S). In this paper, we prove that ifS is a semilattice of completely 0-simple semigroups and completely simple semigroups, then the semigroup ringRS possesses an identity iff so doesR(E(S)); especially, the result is true forS being a completely regular semigroup. 相似文献
17.
LetG be a quasisimple Chevalley group. We give an upper bound for the covering number cn(G) which is linear in the rank ofG, i.e. we give a constantd such that for every noncentral conjugacy classC ofG we haveC
rd
=G, wherer=rankG.
Research supported in part by NSERC Canada Grant A7251.
Research supported in part by the Hermann Minkowski-Minerva Center for Geometry at Tel Aviv University. 相似文献
18.
LetS be a bounded region inR
N and let ℊ={S
i}
i
=1/m
be a partition ofS into a finite number of subsets having piecewiseC
2 boundaries. We assume that whereC
2 segments of the boundaries meet, the angle subtended by tangents to these segments at the point of contact is bounded away
from 0. Letτ:S →S be piecewiseC
2 on ℊ and expanding in the sense that there exists 0<σ< 1 such that for anyi=1, 2, ...,m, ‖Dτ
i
−1
‖<σ, whereDτ
i
−1
is the derivative matrix ofτ
i
−1
and ‖ ‖ is the euclidean matrix norm. The main result provides an upper bound onσ which guarantees the existence of an absolutely continuous invariant measure forτ.
The research of the second author was supported by NSERC and FCAR grants. 相似文献
19.
Frank Gerth III 《manuscripta mathematica》1991,70(1):39-50
Letp be an odd prime number, and letK be a cyclic extension of ℚ(ζ) of degreep, where ζ is a primitivep-th root of unity. LetC
K
be thep-class group ofK, and letr
K
be the minimal number of generators ofC
K
1−σ
as a module over Gal(K/ℚ(ζ)), were σ is a generator of Gal(K/ℚ(ζ)). This paper shows how likely it is forr
K
= 0, 1, 2, … whenp=3, 5, or 7, and describes the obstacle to generalizing these results to regular primesp>7. 相似文献
20.
Sergio Licanic 《Bulletin of the Brazilian Mathematical Society》2000,31(1):113-125
LetF be a holomorphic singular foliation with an invariant compact curveS on a compact algebraic surfaceX. In this work we prove thatF is logarithmic under some generic conditions in the singularities ofF inS.Supported by CNPq (Brazil). 相似文献