The Katětov property for finite degree seminormal functors

A seminormal functor kF enjoys the Katěetov property (K-property) if for every compact set X the hereditary normality of kF(X) implies the metrizability of X. We prove that every seminormal functor of finite degree n>3 enjoys the K-property. On assuming the continuum hypothesis (CH) we characterize the weight preserving seminormal functors with the K-property. We also prove that the nonmetrizable compact set constructed in [1] on assuming CH is a universal counterexample for the K-property in the class of weight preserving seminormal functors.     

On Katětov and Katětov–Blass orders on analytic P-ideals and Borel ideals

Minami–Sakai (Arch Math Logic 55(7–8):883–898, 2016) investigated the cofinal types of the Katětov and the Katětov–Blass orders on the family of all \(F_\sigma \) ideals. In this paper we discuss these orders on analytic P-ideals and Borel ideals. We prove the following:

• The family of all analytic P-ideals has the largest element with respect to the Katětov and the Katětov–Blass orders.
• The family of all Borel ideals is countably upward directed with respect to the Katětov and the Katětov–Blass orders.

In the course of the proof of the latter result, we also prove that for any analytic ideal \(\mathcal {I}\) there is a Borel ideal \(\mathcal {J}\) with \(\mathcal {I} \subseteq \mathcal {J}\).

     

The Katětov-Morita theorem for the dimension of metric frames

The results which appear here are devoted to the dimension theory of metric frames. We begin by characterizing the covering dimension dim of metric frames in terms of special sequences of covers and then prove the fundamental Katětov-Morita Theorem asserting that Ind L = dim L for every metric frame L.     

Some Structural Aspects of the Katětov Order on Borel Ideals

We prove that the Katětov order on Borel ideals (1) contains a copy of \(\mathcal {P}(\omega )/\mathbf {Fin}\), consequently it has increasing and decreasing chains of lenght ??; (2) the sequence F i n ^α (α < ω ₁) is a strictly increasing chain; and (3) in the Cohen model, Katětov order does not contain any increasing nor decreasing chain of length ??, answering a question of Hru?ák (2011).     

An Example of a Fraïssé Class Without a Katětov Functor

We disprove a conjecture from Kubi? and Ma?ulovi? [2] by showing the existence of a Fraïssé class \(\mathcal {C}\) which does not admit a Katětov functor. On the other hand, we show that the automorphism group of the Fraïssé limit of \(\mathcal {C}\) is universal, as it happens in the presence of a Katětov functor.     

The dimension of the finite subsets κ

We answer a question of M. Pouzet by showing that the Dushnik-Miller dimension of the finite subsets of the infinite cardinal ordered by inclusion is ().This paper was written when the first author was visiting the University of Calgary, June, 1995. Research partially supported by Office of Naval Research grant NOOO14-90-1206.Research supported by NSERC grant #69-0982.     

The global dimension of ω-smash coproducts

We mainly study the global dimension of ω-smash coproducts. We show that if H is a Hopf algebra with a bijective antipode S _H , and C _ω ? H denotes the ω-smash coproduct, then gl.dim(C _ω ? H) ≤ gl.dim(C) + gl.dim(H), where gl.dim(H) denotes the global dimension of H as a coalgebra.     

The ϕ-Krull dimension of some commutative extensions

Abstract

In this article, we define the ?-Krull dimension as a generalization of Krull dimension. This property is treated here as a part of a study on some constractions of rings such as direct products, amalgamation of rings, and trivial ring extensions.     

Dense lattice packings of spheres in Euclidean spaces of dimension n⩽16 *

We present a number of lattice packings of equal spheres in ⁿ for n16 For n15, these packings have the same density as the densest known lattice packings. For n=16, the packing described here is denser than the known ones.It should be pointed out that the 16-dimensional lattice described here is equivalent to one found by E. S. Barnes and G. E. Wall, J. Aust. Math. Soc.,1, 47–63 (1959); see also J. Leech and N. J. A. Sloane, Can. J. Math.,23, 718–745 (1971) — Translator.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 82, 144–146, 1979.     

Hausdorff dimension of Lebesgue sets for W α p classes on metric spaces

Let (X, μ, d) be a space of homogeneous type, where d and p are a metric and a measure, respectively, related to each other by the doubling condition with γ > 0. Let W _α ^p (X) be generalized Sobolev classes, let Cap_{α p} (where p > 1 and 0 < α ≤ 1) be the corresponding capacity, and let dim_H be the Hausdorff dimension. We show that the capacity Cap_{α p} is related to the Hausdorff dimension; we also prove that, for each function u ∈ W _α/p (X), p > 1, 0 < a < γ/p, there exists a set E ? X such that dim _H (E) ≤ γ - αp, the limit $$\mathop {\lim }\limits_{r \to + 0} \frac{1}{{\mu (B(x,r))}}\int_{B(x,r)} {u d\mu = u * (x)} $$ exists for each x ∈ X\E, and moreover $$\mathop {\lim }\limits_{r \to + 0} \frac{1}{{\mu (B(x,r))}}\int_{B(x,r)} {\left| {u - u * (x)} \right|^q d\mu = 0, \frac{1}{q} = \frac{1}{p} - \frac{\alpha }{\gamma }.} $$ .     

The characterization of the Triebel-Lizorkin spaces forp=∞

We establish the characterization of the weighted Triebel-Lizorkin spaces for p=∞ by means of a “generalized” Littlewood-Paley function which is based on a kernel satisfying “minimal” moment and Tauberian conditions. This characterization completes earlier work by Bui et al. The definitions of the ? _∞,q ^α spaces are extended in a natural way to ? _∞,∞ ^α and it is proven that this is the same space as ? _∞,∞ ^α , which justifies the standard convention in which the two spaces are defined to be equal. As a consequence, we obtain a new characterization of the Hölder-Zygmund space ? _∞,∞ ^α .     

The radius of convergence of Poincaré series of loop spaces

LetR _S (resp.R _A) be the radius of convergence of the Poincaré series of a loop space (S) (resp. of the Betti-Poincaré series of a noetherian connected graded commutative algebraA over a field of characteristic zero).IfS is a finite 1-connected CW-complex, the rational homotopy Lie algebra ofS is finite dimensional if and only ifR _S-1. OtherwiseR _S<1.There is an easily computable upper bound (usually less than 1) forR _S ifS is formal or coformal.On the other handR _A=+ if and only ifA is a polynomial algebra andR _A=1 if and only ifA is a complete intersection (Golod and Gulliksen conjecture). OtherwiseR _A<1 and the sequence dim Tor _p ^H grows exponentially withp.     

The dimension of subcode-subfields of shortened generalized Reed–Solomon codes

Reed–Solomon (RS) codes are among the most ubiquitous codes due to their good parameters as well as efficient encoding and decoding procedures. However, RS codes suffer from having a fixed length. In many applications where the length is static, the appropriate length can be obtained from an RS code by shortening or puncturing. Generalized Reed–Solomon (GRS) codes are a generalization of RS codes, whose subfield-subcodes (SFSC) are extensively studied. In this paper we show that a particular class of GRS codes produces many SFSC with large dimension. We present two algorithms for searching through these codes and a list of new best-known codes obtained.     

The Sharkovski? Theorem for spaces of measurable functions

We formulate a generalization of the so-called Random Sharkovski? Theorem from paper by Jan Andres, which is the randomized version of the classical Sharkovski? Theorem. We use the method of transformation to deterministic case involving the Kuratowski-Ryll-Nardzewski selection theorem, which allows us to omit the assumption of completeness of the incorporated measurable space. Moreover, we formulate an analogue of the Sharkovski? Theorem for spaces of measurable functions and for Lp-spaces.     

The quartet spaces of G. ’t Hooft

In 1964, G. ’t Hooft postulated three axioms, and proved that every nonempty finite model of them has $4^n$ elements. This note confirms this by showing that every nonempty model can be made into a vector space over the field with four elements. For every pair of different elements $x$ and $y$, the quartet of $x$ and $y$ is the affine line through $x$ and $y$ in this vector space.     

The Ptolemy and Zb?ganu constants of normed spaces

In every inner product space H the Ptolemy inequality holds: the product of the diagonals of a quadrilateral is less than or equal to the sum of the products of the opposite sides. In other words, ‖x−y‖‖z−w‖≤‖x−z‖‖y−w‖+‖z−y‖‖x−w‖ for any points w,x,y,z in H. It is known that for each normed space (X,‖⋅‖), there exists a constant C such that for any w,x,y,z∈X, we have ‖x−y‖‖z−w‖≤C(‖x−z‖‖y−w‖+‖z−y‖‖x−w‖). The smallest such C is called the Ptolemy constant of X and is denoted by C_P(X). We study the relationships between this constant and the geometry of the space X, and hence with metric fixed point theory. In particular, we relate the Ptolemy constant C_P to the Zb?ganu constant C_Z, and prove that if X is a Banach space with , then X has (uniform) normal structure and therefore the fixed point property for nonexpansive mappings. We derive general lower and upper bounds for both C_P and C_Z, and calculate the precise values of these two constants for several normed spaces. We also present a number of conjectures and open problems.     

The 2-factoriality of the O’Grady moduli spaces

The aim of this work is to show that the moduli space M ₁₀ introduced by O’Grady is a 2-factorial variety. Namely, M ₁₀ is the moduli space of semistable sheaves with Mukai vector v: = (2, 0, −2) in H^ev(X,\mathbbZ){H^{ev}(X,\mathbb{Z})} on a projective K3 surface X. As a corollary to our construction, we show that the Donaldson morphism gives a Hodge isometry between v^{^}{v^{\perp}} (sublattice of the Mukai lattice of X) and its image in H² ([(M)\tilde]₁₀, \mathbbZ){H^{2} (\widetilde{M}_{10}, \mathbb{Z})}, lattice with respect to the Beauville form of the 10-dimensional irreducible symplectic manifold [(M)\tilde]₁₀{\widetilde{M}_{10}}, obtained as symplectic resolution of M ₁₀. Similar results are shown for the moduli space M ₆ introduced by O’Grady to produce its 6-dimensional example of irreducible symplectic variety.     

The structure of uniformly Gâteaux smooth Banach spaces

It is shown that a Banach spaceX admits an equivalent uniformly Gateaux smooth norm if and only if the dual ball ofX* in its weak star topology is a uniform Eberlein compact. Supported by AV 101-97-02, AV 1019003 and GA ČR 201-98-1449. Supported by GA ČR 201-98-1449, AV 1019003 and GAUK 1/1998.