arXiv subjects

Jakub Tomaszewski

Publications and source records attributed to Jakub Tomaszewski.

13 recordsLinked to original sources

arXiv2026

On the Hausdorff dimension of the difference sets between typical and normal numbers

We study the Hausdorff dimension of the difference sets between the set of typical numbers, defined via the Erd\H{o}s--R\'enyi law governing the longest run of digits, and the set of numbers normal in base $2$. Although both properties hold for Lebesgue-almost every real number, neither implies the other. The resulting difference sets $\textit{TpcN}\setminus\textit{Normal}$ and $\textit{Normal}\setminus\textit{TpcN}$ are $D_2({\bf \Pi}_3^0)$-complete in the Borel hierarchy. We show that this logical complexity is matched geometrically: both difference sets have full Hausdorff dimension. Unlike the classical Besicovitch-type sets governing single-digit frequencies, normality requires the correct frequency of every finite block simultaneously, and the explicit Moran-set constructions that succeed for simple normality break down under this requirement. We instead establish the dimension via a counting argument bypassing the need for an explicit construction.

math.NT↗

arXiv2026

Measures of maximal entropy for Markovian dynamics on the Gehman dendrite

We study transitive dynamical systems on the Gehman dendrite $\mathcal{G}$ for which the endpoint set $\mathrm{End}(\mathcal{G})$ is invariant. Our goal is to approximate such systems by maps whose measure-theoretic behaviour at maximal entropy is governed by an explicit countable Markov structure. We introduce a class of Markovian maps, encode their dynamics by countable Markov graphs, and use the criteria of Vere-Jones, Gurevich, Salama and Ruette to control the existence of measures of maximal entropy. The main theorem gives two arbitrarily close mixing Markovian perturbations of any given system in the considered class: one has a unique measure of maximal entropy, while the other has none.

math.DS↗

arXiv2025

A few last words on pointwise multipliers of Calderón--Lozanovskiĭ spaces

We will provide a complete description of the space $M(X_F,X_G)$ of pointwise multipliers between two Calderón--Lozanovskiĭ spaces $X_F$ and $X_G$ built upon a rearrangement invariant space $X$ and two Young functions $F$ and $G$. Meeting natural expectations, the space $M(X_F,X_G)$ turns out to be another Calderón--Lozanovskiĭ space $X_{G \ominus F}$ with $G \ominus F$ being the appropriately understood generalized Young conjugate of $G$ with respect to $F$. Nevertheless, our argument is not a mere transplantation of existing techniques and requires a rather delicate analysis of the interplay between the space $X$ and functions $F$ and $G$. Furthermore, as an example to illustrate applications, we will solve the factorization problem for Calderón--Lozanovskiĭ spaces. All this not only complements and improves earlier results (basically giving them the final touch), but also confirms the conjecture formulated by Kolwicz, Leśnik and Maligranda in [Pointwise multipliers of Calderón--Lozanovskiĭ spaces, Math. Nachr. 286 (2012), no. 8-9, 876--907]. We will close this work by formulating a number of open questions that outline a promising panorama for future research.

math.FA↗

arXiv2025

On entropy of pure mixing maps on dendrites

For every $0<\alpha\le\infty$ we construct a continuous pure mixing map (topologically mixing, but not exact) on the Gehman dendrite with topological entropy $\alpha$. It has been previously shown by \v{S}pitalsk\'y that there are exact maps on the Gehman dendrite with arbitrarily low positive topological entropy. Together, these results show that the entropy of maps on the Gehman dendrite does not exhibit the paradoxical behaviour reported for graph maps, where the infimum of the topological entropy of exact maps is strictly smaller than the infimum of the entropy of pure mixing maps. The latter result, stated in terms of popular notions of chaos, says that for maps on graphs, lower entropy implies stronger Devaney chaos. The conclusion of this paper says that lower entropy does not force stronger chaos for maps of the Gehman dendrite.

math.DS↗

arXiv2024

Cantor subsystems on the Gehman dendrite

In the present note we focus on dynamics on the Gehman dendrite $\mathcal{G}$. It is well-known that the set of its endpoints is homeomorphic to a standard Cantor ternary set. For any given surjective Cantor system $\mathcal{C}$ we provide constructions of (i) a mixing but not exact and (ii) an exact map on $\mathcal{G}$, such that in both cases the subsystem formed by $\text{End}(\mathcal{G})$ is conjugate to the initially chosen system on $\mathcal{C}$.

math.DS↗

arXiv2024

Arithmetic, interpolation and factorization of amalgams

Building upon Bennett's and Grosse-Erdmann's ideas falling under the conceptual umbrella of factorization of inequalities, we propose a unified approach towards the structure of certain Banach ideal spaces defined in terms of the least decreasing majorant. The key to our results, and, it seems, the main novelty in general, is the synthesis of discretization process, usually called the blocking technique, along with some tools from the interpolation theory. This blend allows us to obtain an abstract versions of several remarkable results proposed by Bennett and to show certain phenomena in new, somehow more complete perspective. Furthermore, with the help of technology we have developed, we re-prove and sometimes also improve many more recent results belonging to this circle of ideas.

math.FA↗

arXiv2024

Borel complexity of the set of typical numbers

In the present note we study the interrelations between the sets of so-called typical numbers and numbers that are normal in base two. Employing results by Nakai and Shiokawa, we exhibit examples of numbers that belong to one set but do not belong to the other and vice versa. Moreover, we demonstrate the set of typical numbers is $Π_3^0$ in the Borel hierarchy, i.e., it can be expressed as the union of countably many $F_σ\text{-sets.}$ Using the result by Ki and Linton that asserts the same for normal numbers, we examine the Borel complexity of the set of typical numbers that are not normal, proving that it belongs to the $Δ_4^0$ class.

math.LO↗

arXiv2022

Essential norms of pointwise multipliers in the non-algebraic setting

Motivated by some recent results, but also referring to recognized classics, we compute the essential norm and the weak essential norm of multiplication operators acting between two distinct K{\" o}the spaces both defined over the same $\sigma$-finite measure space. A by-product of the technology we have developed here are some applications to Banach sequence spaces related to decreasing functions and to Banach spaces of analytic functions on the unit disc, in particular, Hardy spaces. We will close our work with some specific examples illustrating the previously obtained results including Musielak--Orlicz sequence spaces (in particular, Nakano sequence spaces) as well as Lorentz and Marcinkiewicz sequence spaces.

math.FA↗

arXiv2021

Quotients, $\ell_\infty$ and abstract Cesàro spaces

Investigating some re-arrangement properties of the norm in the quotient spaces $X/X_a$ we determine the properties of the spaces $X$ guaranteeing the existence of a lattice isometric copy of $\ell_\infty$ in the abstract Cesàro spaces $CX$.

math.FA↗

arXiv2020

Pointwise multipliers of Musielak--Orlicz spaces and factorization

We prove that the space of pointwise multipliers between two distinct Musielak--Orlicz spaces is another Musielak-Orlicz space and the function defining it is given by an appropriately generalized Legendre transform. In particular, we obtain characterization of pointwise multipliers between Nakano spaces. We also discuss factorization problem for Musielak-Orlicz spaces and exhibit some differences between Orlicz and Musielak-Orlicz cases.

math.FA↗

arXiv2019

Weakly compact sets and weakly compact pointwise multipliers in Banach function lattices

We prove that the class of Banach function lattices in which all relatively weakly compact sets are equi-integrable sets (i.e. spaces satisfying the Dunford-Pettis criterion) coincides with the class of 1-disjointly homogeneous Banach lattices. A new examples of such spaces are provided. Furthermore, it is shown that Dunford-Pettis criterion is equivalent to de la Vallee Poussin criterion in all rearrangement invariant spaces on the interval. Finally, the results are applied to characterize weakly compact pointwise multipliers between Banach function lattices.

math.FA↗

arXiv2017

Local approach to order continuity in Cesàro function spaces

The goal of this paper is to present a complete characterisation of points of order continuity in abstract Cesàro function spaces $CX$ for $X$ being a symmetric function space. Under some additional assumptions mentioned result takes the form $(CX)_a = C(X_a)$. We also find simple equivalent condition for this equality which in the case of $I=[0,1]$ comes to $X\neq L^\infty$. Furthermore, we prove that $X$ is order continuous if and only if $CX$ is, under assumption that the Cesàro operator is bounded on $X$. This result is applied to particular spaces, namely: Cesàro-Orlicz function spaces, Cesàro-Lorentz function spaces and Cesàro-Marcinkiewicz function spaces to get criteria for OC-points.

math.FA↗

arXiv2016

Pointwise multipliers of Orlicz function spaces and factorization

In the paper we find representation of the space of pointwise multipliers between two Orlicz function spaces, which appears to be another Orlicz space and the formula for the Young function generating this space is given. Further, we apply this result to find necessary and suffcient conditions for factorization of Orlicz function spaces.

math.FA↗