Hilbert 13: Are there are any genuine continuous multivariate real-valued functions?
- Authors: Morris, Sidney
- Date: 2021
- Type: Text , Journal article
- Relation: Bulletin of the American Mathematical Society Vol. 58, no. 1 (2021), p. 107-118
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- Description: This article begins with a provocative question: Are there any genuine continuous multivariate real-valued functions? This may seem to be a silly question, but it is in essence what David Hilbert asked as one of the 23 problems he posed at the second International Congress of Mathematicians, held in Paris in 1900. These problems guided a large portion of the research in mathematics of the 20th century. Hilbert’s 13th problem conjectured that there exists a continuous function (Formula presented), where (Formula presented), which cannot be expressed in terms of composition and addition of continuous functions from ℝ2 → ℝ, that is, as composition and addition of continuous real-valued functions of two variables. It took over 50 years to prove that Hilbert’s conjecture is false. This article discusses the solution. © 2021. American Mathematical Society.
Embeddings of free topological vector spaces
- Authors: Leiderman, Arkady , Morris, Sidney
- Date: 2020
- Type: Text , Journal article
- Relation: Bulletin of the Australian Mathematical Society Vol. 101, no. 2 (2020), p. 311-324
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- Description: It is proved that the free topological vector space contains an isomorphic copy of the free topological vector space for every finite-dimensional cube , thereby answering an open question in the literature. We show that this result cannot be extended from the closed unit interval to general metrisable spaces. Indeed, we prove that the free topological vector space does not even have a vector subspace isomorphic as a topological vector space to , where is a Cook continuum, which is a one-dimensional compact metric space. This is also shown to be the case for a rigid Bernstein set, which is a zero-dimensional subspace of the real line. © 2019 Australian Mathematical Publishing Association Inc..
A remark on the separable quotient problem for topological groups
- Authors: Morris, Sidney
- Date: 2019
- Type: Text , Journal article
- Relation: Bulletin of the Australian Mathematical Society Vol. 100, no. 3 (Dec 2019), p. 453-457
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- Description: The Banach-Mazur separable quotient problem asks whether every infinite-dimensional Banach space B has a quotient space that is an infinite-dimensional separable Banach space. The question has remained open for over 80 years, although an affirmative answer is known in special cases such as when B is reflexive or even a dual of a Banach space. Very recently, it has been shown to be true for dual-like spaces. An analogous problem for topological groups is: Does every infinite-dimensional (in the topological sense) connected (Hausdorff) topological group G have a quotient topological group that is infinite dimensional and metrisable? While this is known to be true if G is the underlying topological group of an infinite-dimensional Banach space, it is shown here to be false even if G is the underlying topological group of an infinite-dimensional locally convex space. Indeed, it is shown that the free topological vector space on any countably infinite k(omega)-space is an infinite-dimensional toplogical vector space which does not have any quotient topological group that is infinite dimensional and metrisable. By contrast, the Graev free abelian topological group and the Graev free topological group on any infinite connected Tychonoff space, both of which are connected topological groups, are shown here to have the tubby torus T-omega, which is an infinite-dimensional metrisable group, as a quotient group.
A topological group observation on the Banach-Mazur separable quotient problem
- Authors: Gabriyelyan, Saak , Morris, Sidney
- Date: 2019
- Type: Text , Journal article
- Relation: Topology and Its Applications Vol. 259, no. (2019), p. 283-286
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- Description: The Separable Quotient Problem of Banach and Mazur asks if every infinite-dimensional Banach space has an infinite-dimensional separable quotient Banach space. It has remained unsolved for 85 years but has been answered in the affirmative for special cases such as reflexive Banach spaces. An affirmative answer to the Separable Quotient Problem would obviously imply that every infinite-dimensional Banach space has a quotient topological group which is separable, metrizable, and infinite-dimensional in the sense of topology. In this paper it is proved that every infinite-dimensional Banach space has as a quotient group the separable metrizable infinite-dimensional topological group, T
Embedding of the free abelian topological group A (X ⊕ X) into A (X)
- Authors: Krupski, Mikolaj , Leiderman, Arkady , Morris, Sidney
- Date: 2019
- Type: Text , Journal article
- Relation: Mathematika Vol. 65, no. 3 (2019), p. 708-718
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- Description: We consider the following question: for which metrizable separable spaces X does the free abelian topological group A (X ⊕ X) isomorphically embed into A (X). While for many natural spaces X such an embedding exists, our main result shows that if X is a Cook continuum or X is a rigid Bernstein set, then A(X ⊕ X) does not embed into A(X) as a topological subgroup. The analogous statement is true for the free boolean group B (X).
- Description: We consider the following question: for which metrizable separable spaces X does the free abelian topological group A (X
Embedding into free topological vector spaces on compact metrizable spaces
- Authors: Gabriyelyan, Saak , Morris, Sidney
- Date: 2018
- Type: Text , Journal article
- Relation: Topology and its Applications Vol. 233, no. (2018), p. 33-43
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- Description: For a Tychonoff space X, let V(X) be the free topological vector space over X. Denote by I, G, Q and Sk the closed unit interval, the Cantor space, the Hilbert cube Q=IN and the k-dimensional unit sphere for k
Subspaces of the free topological vector space on the unit interval
- Authors: Gabriyelyan, Saak , Morris, Sidney
- Date: 2018
- Type: Text , Journal article
- Relation: Bulletin of the Australian Mathematical Society Vol. 97, no. 1 (2018), p. 110-118
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- Description: For a Tychonoff space X, let V(X) be the free topological vector space over X, A(X) the free abelian topological group over X and I the unit interval with its usual topology. It is proved here that if X is a subspace of I, then the following are equivalent: V(X) can be embedded in V(I) as a topological vector subspace; A(X) can be embedded in A(I) as a topological subgroup; X is locally compact. © 2017 Australian Mathematical Publishing Association Inc..
Density character of subgroups of topological groups
- Authors: Leiderman, Arkady , Morris, Sidney , Tkachenko, Mikhail
- Date: 2017
- Type: Text , Journal article
- Relation: Transactions of the American Mathematical Society Vol. 369, no. 8 (2017), p. 5645-5664
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- Description: We give a complete characterization of subgroups of separable topological groups. Then we show that the following conditions are equivalent for an omega-narrow topological group G: (i) G is homeomorphic to a subspace of a separable regular space; (ii) G is topologically isomorphic to a subgroup of a separable topological group; (iii) G is topologically isomorphic to a closed subgroup of a separable path-connected, locally path-connected topological group. A pro-Lie group is a projective limit of finite-dimensional Lie groups. We prove here that an almost connected pro-Lie group is separable if and only if its weight is not greater than the cardinality c of the continuum. It is deduced from this that an almost connected pro-Lie group is separable if and only if it is homeomorphic to a subspace of a separable Hausdorff space. It is also proved that a locally compact (even feathered) topological group G which is a subgroup of a separable Hausdorff topological group is separable, but the conclusion is false if it is assumed only that G is homeomorphic to a subspace of a separable Tychonoff space. We show that every precompact (abelian) topological group of weight less than or equal to c is topologically isomorphic to a closed subgroup of a separable pseudocompact (abelian) group of weight c. This result implies that there is a wealth of closed non-separable subgroups of separable pseudocompact groups. An example is also presented under the Continuum Hypothesis of a separable countably compact abelian group which contains a non-separable closed subgroup.
Free topological vector spaces
- Authors: Gabriyelyan, Saak , Morris, Sidney
- Date: 2017
- Type: Text , Journal article
- Relation: Topology and its Applications Vol. 223, no. (2017), p. 30-49
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- Description: In this paper the free topological vector space V(X) over a Tychonoff space X is defined and studied. It is proved that V(X) is a kω-space if and only if X is a kω-space. If X is infinite, then V(X) contains a closed vector subspace which is topologically isomorphic to V(N). It is proved that for X a k-space, the free topological vector space V(X) is locally convex if and only if X is discrete and countable. The free topological vector space V(X) is shown to be metrizable if and only if X is finite if and only if V(X) is locally compact. Further, V(X) is a cosmic space if and only if X is a cosmic space if and only if the free locally convex space L(X) on X is a cosmic space. If a sequential (for example, metrizable) space Y is such that the free locally convex space L(Y) embeds as a subspace of V(X), then Y is a discrete space. It is proved that V(X) is a barreled topological vector space if and only if X is discrete. This result is applied to free locally convex spaces L(X) over a Tychonoff space X by showing that: (1) L(X) is quasibarreled if and only if L(X) is barreled if and only if X is discrete, and (2) L(X) is a Baire space if and only if X is finite. © 2017 Elsevier B.V.
Nonseparable closed vector subspaces of separable topological vector spaces
- Authors: Kakol, Jerzy , Leiderman, Arkady , Morris, Sidney
- Date: 2017
- Type: Text , Journal article
- Relation: Monatshefte Fur Mathematik Vol. 182, no. 1 (2017), p. 39-47
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- Description: In 1983 P. Domanski investigated the question: For which separable topological vector spaces E, does the separable space have a nonseparable closed vector subspace, where is the cardinality of the continuum? He provided a partial answer, proving that every separable topological vector space whose completion is not q-minimal (in particular, every separable infinite-dimensional Banach space) E has this property. Using a result of S.A. Saxon, we show that for a separable locally convex space (lcs) E, the product space has a nonseparable closed vector subspace if and only if E does not have the weak topology. On the other hand, we prove that every metrizable vector subspace of the product of any number of separable Hausdorff lcs is separable. We show however that for the classical Michael line the space of all continuous real-valued functions on endowed with the pointwise convergence topology, contains a nonseparable closed vector subspace while is separable.
- Description: In 1983 P. DomaA"ski investigated the question: For which separable topological vector spaces E, does the separable space have a nonseparable closed vector subspace, where is the cardinality of the continuum? He provided a partial answer, proving that every separable topological vector space whose completion is not q-minimal (in particular, every separable infinite-dimensional Banach space) E has this property. Using a result of S.A. Saxon, we show that for a separable locally convex space (lcs) E, the product space has a nonseparable closed vector subspace if and only if E does not have the weak topology. On the other hand, we prove that every metrizable vector subspace of the product of any number of separable Hausdorff lcs is separable. We show however that for the classical Michael line the space of all continuous real-valued functions on endowed with the pointwise convergence topology, contains a nonseparable closed vector subspace while is separable.
On varieties of Abelian topological groups with coproducts
- Authors: Gabriyelyan, Saak , Morris, Sidney
- Date: 2017
- Type: Text , Journal article
- Relation: Bulletin of the Australian Mathematical Society Vol. 95, no. 1 (2017), p. 54-65
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- Description: A class of abelian topological groups was previously defined to be a variety of topological groups with coproducts if it is closed under forming subgroups, quotients, products and coproducts in the category of all abelian topological groups and continuous homomorphisms. This extended research on varieties of topological groups initiated by the second author. The key to describing varieties of topological groups generated by various classes was proving that all topological groups in the variety are a quotient of a subgroup of a product of groups in the generating class. This paper analyses generating varieties of topological groups with coproducts. It focuses on the interplay between forming products and coproducts. It is proved that the variety of topological groups with coproducts generated by all discrete groups contains topological groups which cannot be expressed as a quotient of a subgroup of a product of a coproduct of discrete groups. It is proved that the variety of topological groups with coproducts generated by any infinite-dimensional Hilbert space contains all infinite-dimensional Hilbert spaces, answering an open question. This contrasts with the result that a variety of topological groups generated by a topological group does not contain any infinite-dimensional Hilbert space of greater cardinality. © 2016 Australian Mathematical Publishing Association Inc..
An open mapping theorem
- Authors: Gabriyelyan, Saak , Morris, Sidney
- Date: 2016
- Type: Text , Journal article
- Relation: Bulletin of the Australian Mathematical Society Vol. 94, no. 1 (2016), p. 65-69
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- Description: It is proved that any surjective morphism f : Z(k) -> K onto a locally compact group K is open for every cardinal k. This answers a question posed by Hofmann and the second author.
Nonmeasurable subgroups of compact groups
- Authors: Hernández, Salvador , Hofmann, Karl , Morris, Sidney
- Date: 2016
- Type: Text , Journal article
- Relation: Journal of Group Theory Vol. 19, no. 1 (2016), p. 179-189
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- Description: In 1985 S. Saeki and K. Stromberg published the following question: Does every infinite compact group have a subgroup which is not Haar measurable? An affirmative answer is given for all compact groups with the exception of some metric profinite groups which are almost perfect and strongly complete. In this spirit it is also shown that every compact group contains a non-Borel subgroup. © 2016 by De Gruyter 2016 Generalitat Valenciana PROMETEO/2014/062 We are grateful for our referee's useful comments. In particular, the suggestion that originally we had overlooked [Pacific J. Math. 116 (1985), 217-241] shortened the proof of Theorem 4.3 considerably.
Varieties of abelian topological groups with coproducts
- Authors: Gabriyelyan, Saak , Leiderman, Arkady , Morris, Sidney
- Date: 2015
- Type: Text , Journal article
- Relation: Algebra Universalis Vol. 74, no. 3-4 (2015), p. 241-251
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- Description: Varieties of groups, introduced in the 1930s by Garret Birkhoff and B.H. Neumann, are defined as classes of groups satisfying certain laws or equivalently as classes of groups closed under the formation of subgroups, quotient groups, and arbitrary cartesian products. In the 1960s the third author introduced varieties of topological groups as classes of (not necessarily Hausdorff) topological groups closed under subgroups, quotient groups and cartesian products with the Tychonoff topology. While there is only a countable number of varieties of abelian groups, there is a proper class of varieties of abelian topological groups. We observe that while every variety of abelian groups is closed under abelian coproducts, varieties of abelian topological groups are in general not closed under abelian coproducts with the coproduct topology. So this paper studies varieties of abelian topological groups which are also closed under abelian coproducts with the coproduct topology. Noting that the variety of all abelian groups is singly generated, that is, it is the smallest variety containing some particular group, but that the variety of all abelian topological groups is not singly generated, it is proved here that the variety of all abelian topological groups with coproducts is indeed singly generated. There is much literature describing varieties of topological groups generated by various classical topological groups, and the study of varieties with coproducts generated by particular classical topological groups is begun here. Some nice results are obtained about those varieties of abelian topological groups with coproducts which are also closed with regard to forming Pontryagin dual groups. © 2015, Springer Basel.
The weights of closed subgroups of a locally compact group
- Authors: Hernández, Salvador , Hofmann, Karl , Morris, Sidney
- Date: 2012
- Type: Text , Journal article
- Relation: Journal of Group Theory Vol. 15, no. 5 (2012), p. 613-630
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- Description: Let G be an infinite locally compact group and let n be a cardinal satisfying n 0 ≤ n ≤ w(G) for the weight w(G) of G. It is shown that there is a closed subgroup N of G with w(N) = n. Sample consequences are: (1) Every infinite compact group contains an infinite closed metric subgroup. (2) For a locally compact group G and n a cardinal satisfying n 0 ≤ n ≤ w
- Description: 2003010570
The structure of almost connected pro-lie groups
- Authors: Hofmann, Karl , Morris, Sidney
- Date: 2011
- Type: Text , Journal article
- Relation: Journal of Lie Theory Vol. 21, no. 2 (2011), p. 347-383
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- Description: Recalling that a topological group G is said to be almost connected if the quotient group G=G0 is compact, where G0 is the connected component of the identity, we prove that for an almost connected pro-Lie group G, there exists a compact zero-dimensional, that is, profinite, subgroup D of G such that G = G0D. Further for such a group G, there are sets I , J , a compact connected semisimple group S , and a compact connected abelian group A such that G and ℝI × (ℤ=2ℤ)J × S × A are homeomorphic. En route to this powerful structure theorem it is shown that the compact open topology makes the automorphism group Aut g of a semisimple pro-Lie algebra g a topological group in which the identity component (Aut g)0 is exactly the group Inn g of inner automorphisms. In this situation, Inn(G) has a totally disconnected semidirect complement
Iwasawa's local splitting theorem for pro-Lie groups
- Authors: Hofmann, Karl , Morris, Sidney
- Date: 2008
- Type: Text , Journal article
- Relation: Forum Mathematicum Vol. 20, no. 4 (2008), p. 607-629
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- Description: If the nilradical () of the Lie algebra of a pro-Lie group G is finite dimensional modulo the center (), then every identity neighborhood U of G contains a closed normal subgroup N such that G/N is a Lie group and G and N × G/N are locally isomorphic. © Walter de Gruyter 2008.
- Description: C1
On the pro-lie group theorem and the closed subgroup theorem
- Authors: Hofmann, Karl , Morris, Sidney
- Date: 2008
- Type: Text , Journal article
- Relation: Journal of Lie Theory Vol. 18, no. 2 (2008), p. 383-390
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- Description: Let H and M be closed normal subgroups of a pro-Lie group G and assume that H is connected and that G/M is a Lie group. Then there is a closed normal subgroup N of G such that N ? M, that G/N is a Lie group, and that HN is closed in G. As a consequence, H/(H ? N) ? HN/N is an isomorphism of Lie groups. © 2008 Heldermann Verlag.
- Description: C1
An open mapping theorem for pro-Lie groups
- Authors: Hofmann, Karl , Morris, Sidney
- Date: 2007
- Type: Text , Journal article
- Relation: Journal of the Australian Mathematical Society Vol. 83, no. 1 (2007), p. 55-77
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- Description: A pro-Lie group is a projective limit of finite dimensional Lie groups. It is proved that a surjective continuous group homomorphism between connected pro-Lie groups is open. In fact this remains true for almost connected pro-Lie groups where a topological group is called almost connected if the factor group modulo the identity component is compact. As consequences we get a Closed Graph Theorem and the validity of the Second Isomorphism Theorem for pro-Lie groups in the almost connected context. © 2007 Australian Mathematical Society.
- Description: C1
- Description: 2003005492
Open mapping theorem for topological groups
- Authors: Hofmann, Karl , Morris, Sidney
- Date: 2007
- Type: Text , Journal article
- Relation: Topology Proceedings Vol. 31, no. 2 (2007), p. 533-551
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- Description: We survey sufficient conditions that force a surjective continuous homomorphism between topological groups to be open. We present the shortest proof yet of an open mapping theorem between projective limits of finite dimensional Lie groups.
- Description: C1
- Description: 2003005915