共查询到20条相似文献,搜索用时 15 毫秒
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Let S be a pre-Hilbert space. We study quasi-splitting subspaces of S and compare the class of such subspaces, denoted by Eq(S), with that of splitting subspaces E(S). In [D. Buhagiar, E. Chetcuti, Quasi splitting subspaces in a pre-Hilbert space, Math. Nachr. 280 (5-6) (2007) 479-484] it is proved that if S has a non-zero finite codimension in its completion, then Eq(S)≠E(S). In the present paper it is shown that if S has a total orthonormal system, then Eq(S)=E(S) implies completeness of S. In view of this result, it is natural to study the problem of the existence of a total orthonormal system in a pre-Hilbert space. In particular, it is proved that if every algebraic complement of S in its completion is separable, then S has a total orthonormal system. 相似文献
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In this note we give a measure-theoretic criterion for the completeness of an inner product space. We show that an inner product space S is complete if and only if there exists a -additive state on C(S), the orthomodular poset of complete-cocomplete subspaces of S. We then consider the problem of whether every state on E(S), the class of splitting subspaces of S, can be extended to a Hilbertian state on E(
); we show that for the dense hyperplane S (of a separable Hilbert space) constructed by P. Pták and H. Weber in Proc. Am. Math. Soc. 129 (2001), 2111–2117, every state on E(S) is a restriction of a state on E(
).This revised version was published online in April 2005 with a corrected missing date string. 相似文献
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K. Alster 《Topology and its Applications》2009,156(7):1345-1347
We prove that if X is a paracompact space which has a neighborhood assignment x→Hx such that for each y∈X the closure of the set is compact then the products T×X, for every paracompact space T, and Xω are paracompact. The first result answers a problem of H. Junnila. 相似文献
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L. Brian Lawrence 《Transactions of the American Mathematical Society》1998,350(8):3055-3064
Working in ZFC, we prove that for every zero-dimensional subspace of the real line, the Tychonoff power is homogeneous ( denotes the nonnegative integers). It then follows as a corollary that is homogeneous whenever is a separable zero-dimensional metrizable space. The question of homogeneity in powers of this type was first raised by Ben Fitzpatrick, and was subsequently popularized by Gary Gruenhage and Hao-xuan Zhou.
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In this paper,we prove that the general product Hardy operators are bounded from the product Hardy space H1/n ( Rm1 ×…× Rmn ) to L 1 ( RΣni=1 mi). 相似文献
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Let be a cardinal number with the usual order topology. We prove that all subspaces of 2 are weakly sequentially complete and, as a corollary, all subspaces of
are sequentially complete. Moreover we show that a subspace of (1 + 1)2 need not be sequentially complete, but note that X = A × B is sequentially complete whenever A and B are subspaces of . 相似文献
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L. Brian Lawrence 《Transactions of the American Mathematical Society》1996,348(1):187-203
We prove in ZFC that the box product of many copies of is neither normal nor collectionwise Hausdorff. As an addendum to the proof, we show that if the cardinality of the continuum is , then these properties also fail in the closed subspace consisting of all functions which assume the value on all but countably many indices.
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Karl Friedrich Siburg Pavel A. Stoimenov 《Journal of Mathematical Analysis and Applications》2008,344(1):429-439
We introduce a scalar product for n-dimensional copulas, based on the Sobolev scalar product for W1,2-functions. The corresponding norm has quite remarkable properties and provides a new, geometric framework for copulas. We show that, in the bivariate case, it measures invertibility properties of copulas with respect to the ∗-operation introduced by Darsow et al. (1992). The unique copula of minimal norm is the null element for the ∗-operation, whereas the copulas of maximal norm are precisely the invertible elements. 相似文献
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G. Chelidze 《Journal of Mathematical Analysis and Applications》2004,298(1):106-113
We consider a real function which depends on the distances between a variable point and the points of a finite subset A of a linear normed space X. We show that X is an inner product space if this function attains its local minimum on a barycenter of points of A with well-chosen weights. Our result generalizes classical results about characterization of inner product spaces and answers a question of R. Durier, which was posed in his article [J. Math. Anal. Appl. 207 (1997) 220-239]. 相似文献
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We use the Weierstrass σ-function associated with a lattice in the complex plane to construct finite dimensional zero-based subspaces and quasi-invariant subspaces of given index in the Bargmann-Fock space. 相似文献
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We study Hausdorff operators on the product Besov space B01,1 (Rn × Rm) and on the local product Hardy space h1 (Rn × Rm).We establish some boundedness criteria for Hausdorff operators on these functio... 相似文献
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Let H2(D2) be the Hardy space over the bidisk. For sequences of Blaschke products {φn(z):−∞<n<∞} and {ψn(w):−∞<n<∞} satisfying some additional conditions, we may define a Rudin type invariant subspace M. We shall determine the rank of H2(D2)?M for the pair of operators and . 相似文献
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仿紧局部cosmic空间的一些性质 总被引:3,自引:0,他引:3
给出仿紧局部cosmic空间的一些特征,建立了仿紧局部cosmic空间的几类序列覆盖L映象的特征,证明了闭L映射和商ss映射保持仿紧局部cosmic空间的性质,此外,还给出仿紧局部cosmic空间的一些映射性质。 相似文献
15.
Several rules known to be valid within the set theory are revisited and considered from the point of view of the question whether they remain satisfied when sets are replaced with subspaces from Cn,1. It is shown that some of the set relationships hold true upon such a replacement, however, there is also an extensive class of relationships whose validity is no longer guaranteed; in this class the commutativity of the orthogonal projectors onto the involved subspaces proves to play an important role. Some related results inspired by probability theory are established as well. 相似文献
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Using the property of being completely Baire, countable dense homogeneity and the perfect set property we will be able, under Martin?s Axiom for countable posets, to distinguish non-principal ultrafilters on ω up to homeomorphism. Here, we identify ultrafilters with subpaces of 2ω in the obvious way. Using the same methods, still under Martin?s Axiom for countable posets, we will construct a non-principal ultrafilter such that is countable dense homogeneous. This consistently answers a question of Hrušák and Zamora Avilés. Finally, we will give some partial results about the relation of such topological properties with the combinatorial property of being a P-point. 相似文献
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Warren B. Moors 《Proceedings of the American Mathematical Society》2006,134(7):2161-2163
In this paper we prove that the product of a Baire space with a metrizable hereditarily Baire space is again a Baire space. This answers a recent question of J. Chaber and R. Pol.
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M. I. Ostrovskii 《Proceedings of the American Mathematical Society》1996,124(7):2005-2012
It is proved that there exist complemented subspaces of countable topological products (locally convex direct sums) of Banach spaces which cannot be represented as topological products (locally convex direct sums) of Banach spaces.
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P. Szewczak 《Topology and its Applications》2011,158(2):177-182
In [3] R. Telgársky (1975) asked: does the first player have a winning strategy in the game G(F,X×X) if the first player has a winning strategy in the game G(F,X)? I give a positive answer to this question and prove that this result is also true for spaces where the first player has a winning strategy in game G(K,X) where K=1, F, C, for σC if X is P-space and for DC if X is collectionwise-normal space. The last result is related to the Telgársky's (1983) conjecture discussed in [1]. These results are not true for infinite product of spaces. 相似文献
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There is a paracompact Q-set space in ZFC 总被引:1,自引:0,他引:1
Zoltan T. Balogh 《Proceedings of the American Mathematical Society》1998,126(6):1827-1833
We construct a paracompact space such that every subset of is an -set, yet is not -discrete. We will construct our space not to have a -diagonal, which answers questions of A.V. Arhangel'skii and D. Shakhmatov on cleavable spaces.