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Let X be an infinite Tychonoff space, and Y be a topological subspace of X. In this paper, we study some covering properties of the subspace Cp(Y|X) of Cp(Y) consisting of those functions f ∈ C (Y) which admit a continuous extension to X equipped with the relative topology of Cp(Y). Among other results, we show that (i) Cp(Y|X) has a fundamental bounded resolution if and only if Y is countable; when X is realcompact and Y is closed in X, we have (ii) if Cp(Y|X) admits a resolution of convex compact sets that swallows the local null sequences in Cp(Y|X), then Y is countable and discrete; (iii) if Cp(Y|X) admits a compact resolution that swallows the compact sets, then Y is also countable and discrete, and, as a corollary, we deduce that Cp(Y|X) admits a compact resolution that swallows the compact sets if and only if Cp(Y|X) is a Polish space. We also prove that (iv) for a metrizable space X, Cp(X) is a quasi-(LB)-space if and only if X is σ-compact, and hence for a subspace Y of X, the space Cp(Y|X) is a quasi-(LB)-space. We include some examples and observations that answer natural questions raised in this paper. [ABSTRACT FROM AUTHOR]

Let $ X $ be an infinite Tychonoff space, and $ Y $ be a topological subspace of $ X $. In this paper, we study some covering properties of the subspace $ C_{p}\left(Y|X\right) $ of $ C_{p}\left(Y\right) $ consisting of those functions $ f\in C\left(Y\right) $ which admit a continuous extension to $ X $ equipped with the relative topology of $ C_{p}\left(Y\right) $. Among other results, we show that $ \left(i\right) $ $ C_{p}(Y|X) $ has a fundamental bounded resolution if and only if $ Y $ is countable; when $ X $ is realcompact and $ Y $ is closed in $ X $, we have $ \left(ii\right) $ if $ C_{p}(Y|X) $ admits a resolution of convex compact sets that swallows the local null sequences in $ C_{p}(Y|X) $, then $ Y $ is countable and discrete; $ \left(iii\right) $ if $ C_{p}(Y|X) $ admits a compact resolution that swallows the compact sets, then $ Y $ is also countable and discrete, and, as a corollary, we deduce that $ C_{p}(Y|X) $ admits a compact resolution that swallows the compact sets if and only if $ C_{p}(Y|X) $ is a Polish space. We also prove that $ \left(iv\right) $ for a metrizable space $ X $, $ C_{p}\left(X\right) $ is a quasi-$ \left(LB\right) $-space if and only if $ X $ is $ \sigma $-compact, and hence for a subspace $ Y $ of $ X $, the space $ C_{p}\left(Y|X\right) $ is a quasi-$ \left(LB\right) $-space. We include some examples and observations that answer natural questions raised in this paper.

We study analytic and Borel subsets defined similarly to the old example of analytic complete set given by Luzin. Luzin's example, which is essentially a subset of the Baire space, is based on the natural partial order on naturals, i.e. division. It consists of sequences which contain increasing subsequence in given order. We consider a variety of sets defined in a similar way. Some of them occurs to be Borel subsets of the Baire space, while others are analytic complete, hence not Borel. In particular, we show that an analogon of Luzin example based on the natural linear order on rationals is analytic complete. We also characterize all countable linear orders having such property. [ABSTRACT FROM AUTHOR]

In this paper, we prove the following result. Let X be a complete metric space of weight and be a set such that . Then there is no continuous bijection of the subspace onto a -compact space. As a result, there is no continuous bijection of the subspace onto a Polish space. Thus, it has been proved that metric compact spaces are not -spaces for any uncountable cardinal number . This result answers the question asked by E.G. Pytkeev in his coauthored work "On the properties of subclasses of weakly dyadic compact sets" to be published in the Siberian Mathematical Journal. [ABSTRACT FROM AUTHOR]

We study the evolution of states of an infinite system of point particles dwelling in a locally compact Polish space X. Each particle produces at random a finite ‘cloud’ of offsprings distributed over X according to some law, and disappears afterward. The system’s states are probability measures on an appropriate space of locally finite counting measures on X. Their evolution is obtained by solving the corresponding Fokker–Planck equation. We prove that this equation has a unique solution and discuss some of its properties. Our pivotal idea of dealing with infinite systems consists in passing to tempered counting measures by imposing appropriate restrictions on the branching. In this approach, we first solve a nonlinear evolution equation in the space of bounded continuous functions on X—so-called log-Laplace equation. Next, we solve the Kolmogorov equation which is then used to solve the Fokker–Planck equation and thus describe the evolution in question. [ABSTRACT FROM AUTHOR]

S. Marcus showed that there is a quasicontinuous function from the interval [0, 1] to R which is not Lebesgue measurable. We prove that if X is either an uncountable Polish space or a locally pathwise connected perfectly normal topological space with at least one non isolated point, then there is a quasicontinuous non Borel measurable function from X to [0, 1]. We also found new conditions under which for every quasicontinuous function there is an equivalent Borel measurable quasicontinuous function. If X is a Baire space and Y is a separable metric space, then every Borel measurable function f : X → Y of the first class is cliquish. [ABSTRACT FROM AUTHOR]

In this paper, we present a new concept of random contraction and prove a coupled random fixed point theorem under this condition which generalizes stochastic Banach contraction principle. Finally, we apply our contraction to obtain a solution of random nonlinear integral equations and we present a numerical example.

Consider a BV function on a Riemannian manifold. What is its differential? And what about the Hessian of a convex function? These questions have clear answers in terms of (co)vector/matrix valued measures if the manifold is the Euclidean space. In more general curved contexts, the same objects can be perfectly understood via charts. However, charts are often unavailable in the less regular setting of metric geometry, where still the questions make sense. In this paper we propose a way to deal with this sort of problems and, more generally, to give a meaning to a concept of 'measure acting in duality with sections of a given bundle', loosely speaking. Despite the generality, several classical results in measure theory like Riesz's and Alexandrov's theorems have a natural counterpart in this setting. Moreover, as we are going to discuss, the notions introduced here provide a unified framework for several key concepts in nonsmooth analysis that have been introduced more than two decades ago, such as: Ambrosio-Kirchheim's metric currents, Cheeger's Sobolev functions and Miranda's BV functions. Not surprisingly, the understanding of the structure of these objects improves with the regularity of the underlying space. We are particularly interested in the case of RCD spaces where, as we will argue, the regularity of several key measures of the type we study nicely matches the known regularity theory for vector fields, resulting in a very effective theory. We expect that the notions developed here will help creating stronger links between differential calculus in Alexandrov spaces (based on Perelman's DC charts) and in RCD ones (based on intrinsic tensor calculus). [ABSTRACT FROM AUTHOR]

Logical characterizations of probabilistic bisimulation and simulation for Labelled Markov Processes were given by Desharnais et al. These results hold for systems defined on analytic state spaces and assume countably many labels in the case of bisimulation and finitely many labels in the case of simulation. We revisit these results by giving simpler and more streamlined proofs. In particular, our proof for simulation has the same structure as the one for bisimulation, relying on a new result of a topological nature. We also propose a new notion of event simulation. Our proofs assume countably many labels, and we show that the logical characterization of bisimulation may fail when there are uncountably many labels. However, with a stronger assumption on the transition functions (continuity instead of just measurability), we regain the logical characterization result for arbitrarily many labels. These results arose from a game-theoretic understanding of probabilistic simulation and bisimulation. [ABSTRACT FROM AUTHOR]