On mixing in infinite measure spaces

Summary Two concepts of mixing for null-preserving transformations are introduced, both coinciding with (strong) mixing if there is a finite invariant measure. The authors believe to offer the correct answer to the old problem of defining mixing in infinite measure spaces. A sequence of sets is called semiremotely trivial if every subsequence contains a further subsequence with trivial remote -algebra (=tail -field). A transformation T is called mixing if (T ^–n A) is semiremotely trivial for every set A of finite measure; completely mixing if this is true for every measurable A. Thus defined mixing is exactly the condition needed to generalize certain theorems holding in finite measure case. For invertible non-singular transformations complete mixing implies the existence of a finite equivalent invariant mixing measure. If no such measure exists, complete mixing implies that for any two probability measures ₁,₂, in total variation norm.Research of this author is supported by the National Science Foundation (U.S.A.) under grant GP 7693.     

On infinite products of non-Archimedean measure spaces

We study generalized ‘probabilistic measures’ taking values in non-Archimedean fields (in particular, fields of p-adic numbers). We prove the theorem on the existence of probability on a product of non-Archimedean probabilistic spaces.     

On grand Lebesgue spaces on sets of infinite measure

We consider grand Lebesgue spaces on sets of infinite measure and study the dependence of these spaces on the choice of the so‐called. We also consider Mikhlin and Marcinkiewicz theorems on Fourier multipliers in the setting of grand spaces.     

On multiparameter ergodic and martingale theorems in infinite measure spaces

Summary A unified proof is given of several ergodic and martingale theorems in infinite measure spaces.The research of this author is in part supported by the National Science Foundation, grant MCS-8301619     

On the entropy of a product endomorphism in infinite measure spaces

Summary In this note, a relationship is established between the entropy, defined by Krengel for an endomorphism of a -finite measure space, and the notion of a spreading partition. This relationship is used to answer in the quasi-finite case a question raised by Krengel concerning the entropy of the product endomorphism on the direct product of a finite and -finite measure space.     

On the ergodic theory of non-integrable functions and infinite measure spaces

We prove a Chow-Robbins type result for an ergodic, non-negative SSSP, and a similar result for transformations preserving infinite measure, which implies that for these transformations, no “absolute” version of Hopf's theorem can hold.     

Cesaro mean convergence of martingale differences in rearrangement invariant spaces

We study the class of r.i. spaces in which Cesaro means of any weakly null martingale difference sequence is strongly null. This property is related to the Banach-Saks property. We show that in classical (separable) r.i. spaces (such as Orlicz, Lorentz and Marcinkiewicz spaces) these properties coincide but this is no longer true for general r.i. spaces. We locate also a class of r.i. spaces having this property where an analogue of the classical Dunford-Pettis characterization of relatively weakly compact subsets in L ₁ holds. Research was partially supported by the ARC and NSF grant DMS-0244515.     

Mapping properties that preserve convergence in measure on finite measure spaces

Given a finite measure space (X,M,μ) and given metric spaces Y and Z, we prove that if is a sequence of arbitrary mappings that converges in outer measure to an M-measurable mapping and if is a mapping that is continuous at each point of the image of f, then the sequence g○fn converges in outer measure to g○f. We must use convergence in outer measure, as opposed to (pure) convergence in measure, because of certain set-theoretic difficulties that arise when one deals with nonseparably valued measurable mappings. We review the nature of these difficulties in order to give appropriate motivation for the stated result.     

On convergence of LAD estimates in autoregression with infinite variance

The least absolute deviation estimates L(N), from N data points, of the autoregressive constants a = (a₁, …, a_q)′ for a stationary autoregressive model, are shown to have the property that N^σ(L(N) ? a) converge to zero in probability, for $\text{σ <}\text{1}\text{α}$, where the disturbances are i.i.d., attracted to a stable law of index α, 1 ≤ α < 2, and satisfy some other conditions.     

Distance of convergence in measure on spaces of measurable functions

Positivity - In this paper we investigate the distance of convergence in measure whenever the measure is not $$sigma $$ -finite and identify the topological coreflection of this approach structure...     

On proximal convergence in uniform spaces

The paper deals with proximal convergence and Leader's theorem, in the constructive theory of uniform apartness spaces. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Generalized Ricci bounds and convergence of metric measure spaces

We introduce and analyze curvature bounds $\underset{?}{\mathbb{C}\mathrm{urv}}(M\text{,}\mathsf{d}\text{,}m)?K$ for metric measure spaces $(M\text{,}\mathsf{d}\text{,}m)$, based on convexity properties of the relative entropy $\mathrm{Ent}(?|m)$. For Riemannian manifolds, $\underset{?}{\mathbb{C}\mathrm{urv}}(M\text{,}\mathsf{d}\text{,}m)?K$ if and only if ${\mathrm{Ric}}_M(\xi \text{,}\xi )?K?{\left|\xi \right|}^2$ for all $\xi \in TM$. We define a complete separable metric $\mathbb{D}$ on the family of all isomorphism classes of normalized metric measure spaces. It has a natural interpretation in terms of mass transportation. Our lower curvature bounds are stable under $\mathbb{D}$-convergence. We also prove that the family of normalized metric measure spaces with doubling constant $?C$ is closed under $\mathbb{D}$-convergence. Moreover, the subfamily of spaces with diameter $?R$ is compact. To cite this article: K.-T. Sturm, C. R. Acad. Sci. Paris, Ser. I 340 (2005).     

On spaces in which the norm convergence coincides with the order convergence

We investigate partially ordered normed vector spaces in which the norm convergence coincides with the order convergence. We consider spaces where the convergences coincide for arbitrary nets and spaces where the convergences coincide only for sequences. We give conditions which characterize such spaces and investigate their properties. In particular, we study the problem of their Dedekind completeness and -completeness.Translated from Matematicheskie Zametki, Vol. 13, No. 2, pp. 259–268, February, 1973.