The Sandwich theorem via Pataraia’s fixed point theorem

Positivity - The Sandwich theorem (König in Archiv der Mathematik 23:500–1972, 1972) yields the existence of a linear functional sandwiched in between a given superlinear functional and...     

Generalizations of Darbo’s fixed point theorem and solvability of integral and differential systems

In this paper, we establish some new generalizations of Darbo’s fixed point theorem for multivalued mappings. Moreover, we prove the existence of solutions for a class of integral equations by Darbo’s fixed point theorem and the existence of solutions for a class of differential inclusions using a generalization of Darbo’s fixed point theorem.     

Around Browder’s fixed point theorem for contractions

We revisit a fixed point theorem for contractions established by Felix Browder in 1968. We show that many definitions of contractive mappings which appeared in the literature after 1968 turn out to be equivalent formulations or even particular cases of Browder’s definition. We also discuss the problem of the existence of approximate fixed points of continuous mappings; in particular, we settle it in the affirmative for Browder contractions. Finally, we recall three problems concerning Browder contractions which remain unsolved. With great respect for Professor Felix E. Browder     

Two refinements of Frink’s metrization theorem and fixed point results for Lipschitzian mappings on quasimetric spaces

Aequationes mathematicae - Quasimetric spaces have been an object of thorough investigation since Frink’s paper appeared in 1937 and various generalisations of the axioms of metric spaces are...     

Mizoguchi–Takahashi’s type common fixed point theorem

Recently Kamran extended the result of Mizoguchi and Takahashi for closed multi-valued mappings and proved a fixed point theorem. In this paper we further extend the result concluded by Kamran and prove a common fixed point theorem by using the concept of lower semi-continuity.     

An extension of Matkowski’s and Wardowski’s fixed point theorems with applications to functional equations

Aequationes mathematicae - In this paper, we prove a fixed point theorem for a system of maps on the finite product of metric spaces. Our result generalizes the result of Matkowski (Bull Acad Pol...     

On Olaleru’s open problem on Gregus fixed point theorem

Let (X, d) be a complete metric space and ${TX \longrightarrow X }$ be a mapping with the property d(Tx, Ty) ≤ ad(x, y) + bd(x, Tx) + cd(y, Ty) + ed(y, Tx) + fd(x, Ty) for all ${x, y \in X}$ , where 0 < a < 1, b, c, e, f ≥ 0, a + b + c + e + f = 1 and b + c > 0. We show that if e + f > 0 then T has a unique fixed point and also if e + f ≥ 0 and X is a closed convex subset of a complete metrizable topological vector space (Y, d), then T has a unique fixed point. These results extend the corresponding results which recently obtained in this field. Finally by using our main results we give an answer to the Olaleru’s open problem.     

Chasles’ fixed point theorem for Euclidean motions

Chasles’ theorem, a classic and important result of kinematics, states that every orientation-preserving isometry of ${\mathbb{R}^3}$ is a screw motion. We show that this is equivalent to the assertion that each proper Euclidean motion that is not a pure translation, acting on the space of oriented lines, has a unique fixed point (the axis of the screw motion). We use that formulation to derive a simple and novel constructive proof of Chasles’ theorem.     

A soft version of the Knaster–Tarski fixed point theorem with applications

In this paper, first, we define a partial order on a soft set (F, A) and introduce some related concepts. Then, using the concept of a soft mapping introduced by Babitha and Sunil (Comput Math Appl 60(7):1840–1849, 2010), a soft version of Knaster–Tarski fixed point theorem is obtained. Some examples are presented to support the concepts introduced and the results proved herein. As an application of our result, we show that the soft Knaster–Tarski fixed point theorem ensures the existence of a soft common fixed point for a commuting family of order-preserving soft mappings.     

Hartman–Wintner’s theorem and its applications

A theorem of Hartman–Wintner enables us to find a nonzero homogeneous polynomial approximate to the difference of two solutions of an elliptic partial differential equation of second order. This theorem plays a crucial role in the study of an umbilical point on each of a special Weingarten surface, a surface with constant anisotropic mean curvature and a Willmore surface. In the present paper, we will survey the roles of Hartman–Wintner’s theorem on these surfaces.     

Generalization of Kummer’s second theorem with applications

The aim of this research paper is to obtain single series expression of

Localized cohomology and some applications of Popa’s cocycle superrigidity theorem

We prove that orbit equivalence of measure preserving ergodic a.e. free actions of a countable group with the relative property (T) is a complete analytic equivalence relation.     

Variational iteration method: Green’s functions and fixed point iterations perspective

The aim of this article is to demonstrate that the variational iteration method “VIM” is in many instances a version of fixed point iteration methods such as Picard’s scheme. In a wide range of problems, the correction functional resulting from the VIM can be interpreted and/or formulated from well-known fixed point strategies using Green’s functions. A number of examples are included to assert the validity of our claim. The test problems include first and higher order initial value problems.     

A generalization of Krasnosel’skii fixed point theorem for sums of compact and contractible maps with application

The existence of a fixed point for the sum of a generalized contraction and a compact map on a closed convex bounded set is proved. The result is applied to a kind of nonlinear integral equations.     

A fixed point theorem in G-metric spaces via α-series

Abstract

In the context of G-metric spaces we prove a common fixed point theorem for a sequence of self mappings using a new concept of α-series.     

A very simple proof of Pascal’s hexagon theorem and some applications

In this article we present a simple and elegant algebraic proof of Pascal’s hexagon theorem which requires only knowledge of basics on conic sections without theory of projective transformations. Also, we provide an efficient algorithm for finding an equation of the conic containing five given points and a criterion for verification whether a set of points is a subset of the conic.