Open Access Published by De Gruyter Open Access

Volume 50 Issue 1

April 2017

Issue of Demonstratio Mathematica

Contents
Journal Overview

Regular Articles

Open Access May 4, 2017

The algebras of bounded and essentially bounded Lebesgue measurable functions

Raymond Mortini, Rudolf Rupp

Page range: 94-99

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Abstract

Let X be a set in ℝ n with positive Lebesgue measure. It is well known that the spectrum of the algebra L ∞ (X) of (equivalence classes) of essentially bounded, complex-valued, measurable functions on X is an extremely disconnected compact Hausdorff space.We show, by elementary methods, that the spectrum M of the algebra ℒ b (X, ℂ) of all bounded measurable functions on X is not extremely disconnected, though totally disconnected. Let ∆ = { δ x : x ∈ X} be the set of point evaluations and let g be the Gelfand topology on M. Then (∆, g) is homeomorphic to (X, Τ dis ),where T dis is the discrete topology. Moreover, ∆ is a dense subset of the spectrum M of ℒ b (X, ℂ). Finally, the hull h(I), (which is homeomorphic to M(L ∞ (X))), of the ideal of all functions in ℒ b (X, ℂ) vanishing almost everywhere on X is a nowhere dense and extremely disconnected subset of the Corona M \ ∆ of ℒ b (X, ℂ).

Open Access May 24, 2017

Diophantine approximations and almost periodic functions

Adam Nawrocki

Page range: 100-104

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Abstract

In this paper we investigate the asymptotic behaviour of the classical continuous and unbounded almost periodic function in the Lebesgue measure.Using diophantine approximations we show that this function can be estimated by functions of polynomial type and we give the best polynomial estimation.

Open Access May 24, 2017

Multiplication operators on the space of functions of bounded variation

Franklin R. Astudillo-Villalba, Julio C. Ramos-Fernández

Page range: 105-115

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Abstract

In this paper,we study the properties of the multiplication operator acting on the bounded variation space BV[0, 1]. In particular,we show the existence of non-null compact multiplication operators on BV[0, 1] and non-invertible Fredholm multiplication operators on BV[0, 1].

Open Access May 24, 2017

Note on strict contractive conditions and common fixed point theorems with application

Ravindra K. Bisht

Page range: 116-118

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Abstract

In this note we point out errors in the proofs of first two theorems contained in Demonstratio Mathematica, Vol. XLVI, no 2, 2013, 405-413. We also rectify the erratic theorems by employing a proper setting.

Open Access May 24, 2017

Rate of Convergence for Ibragimov-Gadjiev-Durrmeyer Operators

Tuncer Acar

Page range: 119-129

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Abstract

The present paper deals with the rate of convergence of the general class of Durrmeyer operators, which are generalization of Ibragimov-Gadjiev operators. The special cases of the operators include somewell known operators as particular cases viz. Szász-Mirakyan-Durrmeyer operators, Baskakov-Durrmeyer operators. Herewe estimate the rate of convergence of Ibragimov-Gadjiev-Durrmeyer operators for functions having derivatives of bounded variation.

Open Access May 24, 2017

Rate of convergence of Szász-beta operators based on q-integers

Pooja Gupta, Purshottam Narain Agrawal

Page range: 130-143

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Abstract

The purpose of this paper is to establish the rate of convergence in terms of the weighted modulus of continuity and Lipschitz type maximal function for the q-Szász-beta operators. We also study the rate of A-statistical convergence. Lastly, we modify these operators using King type approach to obtain better approximation.

Open Access May 24, 2017

On generalized Baskakov-Durrmeyer-Stancu type operators

Angamuthu Sathish Kumar, Zoltán Finta, Purshottam Narain Agrawal

Page range: 144-155

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Abstract

In this paper, we study some local approximation properties of generalized Baskakov-Durrmeyer-Stancu operators. First, we establish a recurrence relation for the central moments of these operators, then we obtain a local direct result in terms of the second order modulus of smoothness. Further, we study the rate of convergence in Lipschitz type space and the weighted approximation properties in terms of the modulus of continuity, respectively. Finally, we investigate the statistical approximation property of the new operators with the aid of a Korovkin type statistical approximation theorem.

Open Access May 24, 2017

Approximation Properties of Ibragimov-Gadjiev-Durrmeyer Operators on Lp (ℝ⁺)

Gülsüm Ulusoy, Ali Aral

Page range: 156-174

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Abstract

We deal with the approximation properties of a new class of positive linear Durrmeyer type operators which offer a reconstruction of integral type operators including well known Durrmeyer operators. This reconstruction allows us to investigate approximation properties of the Durrmeyer operators at the same time. It is first shown that these operators are a positive approximation process in Lp(ℝ + ) . While we are showing this property of the operators we consider the Ditzian-Totik modulus of smoothness and corresponding K-functional. Then, weighted norm convergence, whose proof is based on Korovkin type theorem on Lp(ℝ + ), is given. At the end of the paper we show several examples of classical sequences that can be obtained from the Ibragimov-Gadjiev-Durrmeyer operators.

Open Access August 24, 2017

Approximation by q-analogue of modified Jakimovski-Leviatan-Stancu type operators

Mohammad Mursaleen, Mohammad Nasiruzzaman, Abdul Wafi

Page range: 175-189

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Abstract

In this paper, we introduce the q-analogue of the Jakimovski-Leviatan type modified operators introduced by Atakut with the help of the q-Appell polynomials.We obtain some approximation results via the well-known Korovkin’s theorem for these operators.We also study convergence properties by using the modulus of continuity and the rate of convergence of the operators for functions belonging to the Lipschitz class. Moreover,we study the rate of convergence in terms of modulus of continuity of these operators in aweighted space.

Open Access September 2, 2017

Some fixed point results on G-metric and G_b-metric spaces

Mohammed M.M. Jaradat, Zead Mustafa, Sami Ullah Khan, Muhammad Arshad, Jamshaid Ahmad

Page range: 190-207

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Abstract

The purpose of this paper is to prove some fixed point results using JS-G-contraction on G-metric spaces, also to prove some fixed point results on G b -complete metric space for a new contraction. Our results extend and improve some results in the literature. Moreover, some examples are presented to illustrate the validity of our results.

Open Access September 2, 2017

Multivariate and abstract approximation theory for Banach space valued functions

George A. Anastassiou

Page range: 208-222

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Abstract

Here we study quantitatively the high degree of approximation of sequences of linear operators acting on Banach space valued Fréchet differentiable functions to the unit operator, as well as other basic approximations including those under convexity. These operators are bounded by real positive linear companion operators. The Banach spaces considered here are general and no positivity assumption is made on the initial linear operators for which we study their approximation properties. We derive pointwise and uniform estimates, which imply the approximation of these operators to the unit assuming Fréchet differentiability of functions, and then we continue with basic approximations. At the end we study the special case where the approximated function fulfills a convexity condition resulting into sharp estimates. We give applications to Bernstein operators.

Open Access September 2, 2017

An alternative and easy approach to fixed point results via simulation functions

Stojan Radenovic, Francesca Vetro, Jelena Vujaković

Page range: 223-230

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Abstract

We discuss, extend, improve and enrich results on simulation functions established by several authors. Furthermore, by using Lemma 2.1 of Radenovic et al. [Bull. Iran. Math. Soc., 2012, 38, 625],we get much shorter and nicer proofs than the corresponding ones in the existing literature.

Open Access September 30, 2017

A dimensional restriction for a class of contact manifolds

Eugenia Loiudice

Page range: 231-238

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Abstract

In this work we consider a class of contact manifolds (M, η) with an associated almost contact metric Structure (ϕ, ξ, η, g). This class contains, for example, nearly cosymplectic manifolds and the manifolds in the class C9 ⊕ C10 defined by Chinea and Gonzalez. All manifolds in the class considered turn out to have dimension 4n + 1. Under the assumption that the sectional curvature of the horizontal 2-planes is constant at one point, we obtain that these manifolds must have dimension 5.

Open Access October 20, 2017

Two properties of Müntz spaces

Trond A. Abrahamsen, Aleksander Leraand, André Martiny, Olav Nygaard

Page range: 239-244

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Abstract

We show that Müntz spaces, as subspaces of C[0, 1], contain asymptotically isometric copies of c 0 and that their dual spaces are octahedral.

Open Access October 20, 2017

Derivatives of a polynomial of best approximation and modulus of smoothness in generalized Lebesgue spaces with variable exponent

Sadulla Z. Jafarov

Page range: 245-251

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Abstract

The relation between derivatives of a polynomial of best approximation and the best approximation of the function is investigated in generalized Lebesgue spaces with variable exponent. In addition, the relationship between the fractional modulus of smoothness of the function and its de la Vallée-Poussin sums is studied.

Open Access October 28, 2017

A note on range-kernel uncomplementation

Carlos Kubrusly, Bhagwati Prashad Duggal

Page range: 252-260

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Abstract

This note exhibits a Banach-space operator such that neither the range nor the kernel is complemented both for the operator and its adjoint

Open Access October 28, 2017

Lp-potentials on infinite networks

Kamaleldin Abodayeh, Victor Anandam

Page range: 261-266

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Abstract

Based on the existence of discrete Lp− subharmonic functions, a classification of infinite networks is carried out.

Open Access October 28, 2017

Norm estimates for functions of non-selfadjoint operators nonregular on the convex hull of the spectrum

Michael Gil’

Page range: 267-277

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Abstract

We consider a bounded linear operator A in a Hilbert space with a Hilbert-Schmidt Hermitian component (A − A*)/2i. A sharp norm estimate is established for functions of A nonregular on the convex hull of the spectrum. The logarithm, fractional powers and meromorphic functions of operators are examples of such functions. Our results are based on the existence of a sequence An (n = 1, 2, ...) of finite dimensional operators strongly converging to A, whose spectra belongs to the spectrum of A. Besides, it is shown that the resolvents and holomorphic functions of An strongly converge to the resolvent and corresponding function of A.

Open Access November 24, 2017

Common fixed point theorems via generalized condition (B) in quasi-partial metric space and applications

Anita Tomar, Said Beloul, Ritu Sharma, Shivangi Upadhyay

Page range: 278-298

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Abstract

The aim of this paper is to introduce generalized condition (B) in a quasi-partial metric space acknowledging the notion of Künzi et al. [Künzi H.-P. A., Pajoohesh H., Schellekens M. P., Partial quasi-metrics, Theoret. Comput. Sci., 2006, 365, 237-246] and Karapinar et al. [Karapinar E., Erhan M.,Öztürk A., Fixed point theorems on quasi-partial metric spaces, Math. Comput.Modelling, 2013, 57, 2442-2448] and to establish coincidence and common fixed point theorems for twoweakly compatible pairs of self mappings. In the sequelwe also answer affirmatively two open problems posed by Abbas, Babu and Alemayehu [Abbas M., Babu G. V. R., Alemayehu G. N., On common fixed points of weakly compatible mappings satisfying generalized condition (B), Filomat, 2011, 25(2), 9-19]. Further in the setting of a quasi-partial metric space, the results obtained are utilized to establish the existence and uniqueness of a solution of the integral equation and the functional equation arising in dynamic programming. Our results are also justified by explanatory examples supported with pictographic validations to demonstrate the authenticity of the postulates.

Open Access December 22, 2017

P_β-connectedness in topological spaces

Brij K. Tyagi, Sumit Singh, Manoj Bhardwaj

Page range: 299-308

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Abstract

A new property called P β -connectedness is introduced which is stronger than connectedness and equivalent to pre-connectedness. The properties of this notion are explored and its relationship with other forms of connectedness, for example hyperconnectedness etc. are discussed. Locally pre-indiscrete spaces are defined as the spaces in which pre-open sets are closed. In such spaces connectedness becomes equivalent to pre-connectedness and hence to P β -connectedness, and semi-connectedness becomes equivalent to P β - connectedness. The notion of locally P β -connected space is introduced. The behavior of P β -connectedness under several types of mappings is investigated. An intermediate value theorem is obtained.

Open Access December 22, 2017

Second order evolution equations with nonlocal conditions

Mouffak Benchohra, Juan J. Nieto, Noreddine Rezoug

Page range: 309-319

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Abstract

In this paper, we shall establish sufficient conditions for the existence of solutions for second order semilinear functional evolutions equation with nonlocal conditions in Fréchet spaces. Our approach is based on the concepts of Hausdorff measure, noncompactness and Tikhonoff’s fixed point theorem. We give an example for illustration.

Open Access December 29, 2017

Almost periodic solutions of Volterra difference systems

Halis Can Koyuncuoglu, Murat Adıvar

Page range: 320-329

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Abstract

We study the existence of an almost periodic solution of discrete Volterra systems by means of fixed point theory. Using discrete variant of exponential dichotomy, we provide sufficient conditions for the existence of an almost periodic solution. Hence, we provide an alternative solution for the open problem proposed in the literature.

Open Access December 29, 2017

Concrete minimal 3 × 3 Hermitian matrices and some general cases

Abel H. Klobouk, Alejandro Varela

Page range: 330-350

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Abstract

Given a Hermitian matrix M ∈ M 3 (ℂ) we describe explicitly the real diagonal matrices D M such that ║M + DM║ ≤ ║M + D║ for all real diagonal matrices D ∈ M 3 (ℂ), where ║ · ║ denotes the operator norm. Moreover, we generalize our techniques to some n × n cases.

Open Access December 29, 2017

On the approximation of integrable functions by some special matrix means of Fourier series

Radosława Kranz, Aleksandra Rzepka

Page range: 351-359

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Abstract

The results concerninig pointwise approximation and product of summability methods corresponding to the theorems of Xh. Z. Krasniqi [Poincare J. Anal. Appl., 2014, 1, 1-8] and W. Łenski and B. Szal [Math. Slovaca, 2016, 66(6), 1-12] are generalized. Some special cases are also formulated as corollaries.

Open Access December 29, 2017

Notes on multidimensional fixed-point theorems

Habibulla Akhadkulov, Salmi M. Noorani, Azizan B. Saaban, Fathilah M. Alipiah, Habes Alsamir

Page range: 360-374

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Abstract

In this paper we prove the existence and uniqueness of coincident (fixed) points for nonlinear mappings of any number of arguments under a (ψ, θ, φ)-weak contraction condition without O-compatibility. The obtained results extend, improve and generalize some well-known results in the literature to be discussed below. Moreover, we present an example to show the efficiency of our results.

Special Issue Dedicated to Prof. Heller

Open Access March 30, 2017

Preface to the Special Issue dedicated to Prof. Heller

Leszek Pysiak, Wiesław Sasin

Page range: 1-1

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Open Access April 12, 2017

An introduction to the edition of two Lemaître’s original manuscripts

Catherine de Maere, Dominique Lambert

Page range: 2-27

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Abstract

The aim of this paper is to explain the contributions of G. Lemaître to Spinor Theory. At the end of the paper, we edited also, for the first time two short manuscripts: Spineurs et Quanta and Les spineurs et la physique quantique, written by Lemaître in December 1955 and in January 1956. This edition is a way of honouring Professor Michael Heller because he was the first, with Professor Odon Godart, who discovered, classified and published unedited manuscripts of G. Lemaître.

Open Access April 13, 2017

On Weil homomorphism in locally free sheaves over structured spaces

Ewa Falkiewicz, Wiesław Sasin

Page range: 28-41

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Abstract

Inspired by the work of Heller and Sasin [1], we construct in this paper Weil homomorphism in a locally free sheaf W of ϕ-fields [2] over a structured space. We introduce the notion of G-consistent, linear connection on this sheaf, what allows us to clearly define Chern, Pontrjagin and Euler characteristic classes. We also show proper equalities between those classes.

Open Access April 13, 2017

Multiplicity formulas for representations of transformation groupoids

Artur Giżycki, Leszek Pysiak

Page range: 42-50

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Abstract

We study the representations of transitive transformation groupoids with the aim of generalizing the Mackey theory. Using the Mackey theory and a bijective correspondence between the imprimitivity systems and the representations of a transformation groupoid we derive the irreducibility theory. Then we derive the direct sum decomposition for representations of a groupoid together with the formula for the multiplicity of subrepresentations. We discuss a physical interpretation of this formula. Finally, we prove the claim analogous to the Peter-Weyl theorem for a noncompact transformation groupoid. We show that the representation theory of a transitive transformation groupoids is closely related to the representation theory of a compact groups.

Open Access April 20, 2017

Lyapunov function for cosmological dynamical system

Marek Szydłowski, Adam Krawiec

Page range: 51-55

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Abstract

We prove the asymptotic global stability of the de Sitter solution in the Friedmann-Robertson-Walker conservative and dissipative cosmology. In the proof we construct a Lyapunov function in an exact form and establish its relationship with the first integral of dynamical system determining evolution of the flat Universe. Our result is that de-Sitter solution is asymptotically stable solution for general form of equation of state p = (ρ, H), where dependence on the Hubble function H means that the effect of dissipation are included.

Open Access May 4, 2017

On the geometric nature of the twin paradox in curved spacetimes

Leszek M. Sokołowski

Page range: 56-65

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Abstract

The famous „twin paradox” of special relativity is of purely geometric nature and formulated in curved spacetimes of general relativity motivates investigations of the timelike geodesic structure of these manifolds. Except for the maximally symmetric spacetimes the search for the longest timelike curves is hard, complicated and requires both advanced methods of global Lorentzian geometry and solving the intricate geodesic deviation equation. This article is a theoretical introduction to the problem. First we describe the procedure of determining the locally longest curves; it is algorithmic in the sense of consisting of a small number of definite steps and is effective if the geodesic deviation equation may be solved. Then we discuss the problem of globally maximal timelike curves; due to its nonlocal nature there is no prescription of how to solve it in finite number of steps. In the case of sufficiently high symmetry of the manifold also the globally longest curves may be found. Finally we briefly present some results recently found.

Open Access May 4, 2017

On the Gauss-Bonnet for the quasi-Dirac operators on the sphere

Andrzej Sitarz

Page range: 66-71

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Abstract

We investigate examples of Gauss-Bonnet theorem and the scalar curvature for the two-dimensional commutative sphere with quasi-spectral triples obtained by modifying the order-one condition.

Open Access May 16, 2017

Sasakian structures a foliated approach

Robert A. Wolak

Page range: 72-82

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Abstract

Recent renewed interest in Sasakian manifolds is due mainly to the fact that they can provide examples of generalized Einstein manifolds, manifolds which are of great interest in mathematical models of various aspects of physical phenomena. Sasakian manifolds are odd dimensional counterparts of Kählerian manifolds to which they are closely related. The paper presents a foliated approach to Sasakian manifolds on which the author gave several lectures. The paper concentrates on cohomological properties of Sasakian manifolds and of transversely holomorphic and Kählerian foliations. These properties permit to formulate obstructions to the existence of Sasakian structures on compact manifolds.

Open Access May 16, 2017

Quantum Riemannian geometry of phase space and nonassociativity

Edwin J. Beggs, Shahn Majid

Page range: 83-93

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Abstract

Noncommutative or ‘quantum’ differential geometry has emerged in recent years as a process for quantizing not only a classical space into a noncommutative algebra (as familiar in quantum mechanics) but also differential forms, bundles and Riemannian structures at this level. The data for the algebra quantisation is a classical Poisson bracket while the data for quantum differential forms is a Poisson-compatible connection. We give an introduction to our recent result whereby further classical data such as classical bundles, metrics etc. all become quantised in a canonical ‘functorial’ way at least to 1st order in deformation theory. The theory imposes compatibility conditions between the classical Riemannian and Poisson structures as well as new physics such as typical nonassociativity of the differential structure at 2nd order. We develop in detail the case of ℂℙ n where the commutation relations have the canonical form [w i , w̄ j ] = iλδ ij similar to the proposal of Penrose for quantum twistor space. Our work provides a canonical but ultimately nonassociative differential calculus on this algebra and quantises the metric and Levi-Civita connection at lowest order in λ.

About this journal

Demonstratio Mathematica is a fully peer-reviewed, open access, electronic journal devoted to functional analysis, approximation theory and related topics. The journal presents a forum where all aspects of these problems can be discussed. The journal provides the readers with free, instant, and permanent access to all content worldwide; and the authors with extensive promotion of published articles, long-term preservation, no space constraints and quick online publication.

Demonstratio Mathematica is listed inter alia by Web of Science (ESCI), SCOPUS, MathSciNet and zbMATH. Our standard policy requires each paper to be reviewed by at least two Referees and the peer-review process is single-blind.

The potential topics include (but are not limited to):

Approximation theory and iteration methods
Fixed point theory and methods of computing fixed points
Functional, ordinary and partial differential equations
Nonsmooth analysis, variational analysis and convex analysis
Optimization theory, variational inequalities and complementarity problems

For more detailed list of the potential topics please refer to Instruction for Authors.

The journal considers submissions of different types of articles. "Research Articles" are focused on fundamental theoretical aspects, as well as on significant applications in science, engineering etc. “Communications” are intended to present information of exceptional novelty and exciting results of significant interest to the readers. “Review articles” and “Commentaries”, which present the existing literature on the specific topic from new perspectives, are welcome as well.

Demonstratio Mathematica is subject to an Article Processing Charge (APC). There are no submission charges – Article Processing Charges apply after the acceptance of a manuscript. Authors, who have limited access to funds, may request for a discount. Inquiries concerning APCs should be addressed before or immediately after submission of a paper to the Editorial Office (demonstratio.editorial@degruyter.com). For more details please refer to Article Processing Charges document (in PDF).

Special / Topical Issues:

Development of Fuzzy Sets and Their Extensions
GUEST EDITORS: Željko Stević (University of East Sarajevo, Bosnia and Herzegovina), Yiming Tang (Hefei University of Technology, China), Lei Liu (Liaoning University of Technology, China), Muhammad Gulzar (University of Education Lahore, Pakistan)
DEADLINE FOR SUBMISSIONS: October 16, 2023
2nd International E-Conference on Mathematical and Statistical Sciences: A Selcuk Meeting
GUEST EDITOR: Tuncer Acar (Selçuk University, Turkey)
DEADLINE FOR SUBMISSIONS: August 31, 2023
Dynamic Modeling and Control methods for the Nonlinear system using Artificial Mathematical Intelligence
GUEST EDITORS: B. Nagaraj (Rathinam Group of Institutions, Coimbatore, India), Danilo Pelusi (Communication Engineering, University of Teramo, Italy), Raffaele Mascella (Communication Engineering University of Teramo, Italy)
DEADLINE FOR SUBMISSIONS: July 15, 2023
Recent Developments in Fixed-Point Theory and Applications
GUEST EDITORS: Santosh Kumar (University of Dar es Salaam, Tanzania), Anita Tomar (Sri Dev Suman Uttarakhand University, India), Cristian Chifu (Babes-Bolyai University, Romania), Mohammad Mursaleen (Aligarh Muslim University, India)
DEADLINE FOR SUBMISSIONS: October 10, 2023
On some integral inequalities, integral equations and applications
GUEST EDITORS: Ahmet O. Akdemir (Ağrı İbrahim Çeçen University, Turkey), Maria Alessandra Ragusa (University of Catania, Italy), Nguyen Huy Tuan (Van Lang University, Vietnam)
DEADLINE FOR SUBMISSIONS: October 15, 2023
Nonlinear Evolution Equations and Their Applications
GUEST EDITORS: Praveen Agarwal (Anand International College of Engineering, India), Dumitru Baleanu (Department of Mathematics, Cankaya University, Turkey), Necati Ozdemir (Balikesir University, Turkey), Mohamed S. Osman (Department of Mathematics, Faculty of Science, Cairo University, Egypt)
DEADLINE FOR SUBMISSIONS: August 15, 2023
Mathematics for Artificial intelligence and Artificial intelligence for Mathematics
GUEST EDITORS: Hadi Jahanshahi (University of Manitoba, Canada), Oscar Castillo (Tijuana Institute of Technology, Mexico)
DEADLINE FOR SUBMISSIONS: October 2, 2023
Computational and Numerical Methods for Special Functions
GUEST EDITORS: Serkan Araci (Hasan Kalyoncu University, Turkey), Martin Bohner (Missouri University of Science and Technology, USA), Guotao Wang (Shanxi Normal University, China)
DEADLINE FOR SUBMISSIONS: March 31, 2023.

Volume 50 Issue 1

Issue of Demonstratio Mathematica

The algebras of bounded and essentially bounded Lebesgue measurable functions

Abstract

Diophantine approximations and almost periodic functions

Abstract

Multiplication operators on the space of functions of bounded variation

Abstract

Note on strict contractive conditions and common fixed point theorems with application

Abstract

Rate of Convergence for Ibragimov-Gadjiev-Durrmeyer Operators

Abstract

Rate of convergence of Szász-beta operators based on q-integers

Abstract

On generalized Baskakov-Durrmeyer-Stancu type operators

Abstract

Approximation Properties of Ibragimov-Gadjiev-Durrmeyer Operators on Lp (ℝ+)

Abstract

Approximation by q-analogue of modified Jakimovski-Leviatan-Stancu type operators

Abstract

Some fixed point results on G-metric and Gb-metric spaces

Abstract

Multivariate and abstract approximation theory for Banach space valued functions

Abstract

An alternative and easy approach to fixed point results via simulation functions

Abstract

A dimensional restriction for a class of contact manifolds

Abstract

Two properties of Müntz spaces

Abstract

Derivatives of a polynomial of best approximation and modulus of smoothness in generalized Lebesgue spaces with variable exponent

Abstract

A note on range-kernel uncomplementation

Abstract

Lp-potentials on infinite networks

Abstract

Norm estimates for functions of non-selfadjoint operators nonregular on the convex hull of the spectrum

Abstract

Common fixed point theorems via generalized condition (B) in quasi-partial metric space and applications

Abstract

Pβ-connectedness in topological spaces

Abstract

Second order evolution equations with nonlocal conditions

Abstract

Almost periodic solutions of Volterra difference systems

Abstract

Concrete minimal 3 × 3 Hermitian matrices and some general cases

Abstract

On the approximation of integrable functions by some special matrix means of Fourier series

Abstract

Notes on multidimensional fixed-point theorems

Abstract

Preface to the Special Issue dedicated to Prof. Heller

An introduction to the edition of two Lemaître’s original manuscripts

Abstract

On Weil homomorphism in locally free sheaves over structured spaces

Abstract

Multiplicity formulas for representations of transformation groupoids

Abstract

Lyapunov function for cosmological dynamical system

Abstract

On the geometric nature of the twin paradox in curved spacetimes

Abstract

On the Gauss-Bonnet for the quasi-Dirac operators on the sphere

Abstract

Sasakian structures a foliated approach

Abstract

Quantum Riemannian geometry of phase space and nonassociativity

Abstract

Approximation Properties of Ibragimov-Gadjiev-Durrmeyer Operators on Lp (ℝ⁺)

Some fixed point results on G-metric and G_b-metric spaces

P_β-connectedness in topological spaces