A local duality principle for the Baire classes of functions

A local dual of a Banach space X is a closed subspace of X^∗ that satisfies the properties that the principle of local reflexivity assigns to X as a subspace of X∗∗. We show that, for every ordinal 1?α?ω₁, the spaces Bα[0,1] of bounded Baire functions of class α are local dual spaces of the space M[0,1] of all Borel measures. As a consequence, we derive that each annihilator Bα^⊥[0,1] is the kernel of a norm-one projection.     

Axial Borel functions

A function from the plane to the plane is axial if it does not change one coordinate. We show that every Borel permutation of the plane is a superposition of 11 Borel axial permutations.     

Large null sets in metric spaces

It is shown that every locally compact σ-compact metric space endowed with a Borel measure related to the metric by a natural condition contains sets of measure zero which are extremely large in the sense of cardinality, Hausdorff dimension and Baire category classification.     

Borel hierarchies in infinite products of Polish spaces

Let H be a product of countably infinite number of copies of an uncountable Polish space X. Let Σ_ξ be the class of Borel sets of additive class ξ for the product of copies of the discrete topology on X (the Polish topology on X), and let . We prove in the Lévy-Solovay model that

On the existence of a finite invariant measure

A necessary and sufficient condition is given for a Borel automorphism on a standard Borel space to admit an invariant probability measure.     

Some results on projection of planar sets

In this paper we define certain types of projections of planar sets and study some properties of such projections.     

Gauges of Baire class one functions

Let K be a compact metric space and be a bounded Baire class one function. We proved that for any ε>0 there exists an upper semicontinuous positive function δ of f with finite oscillation index and |f(x)−f(y)|<ε whenever d(x,y)<min{δ(x),δ(y)}.     

Characterization of Generating Ideals in Some Rings of Entire Functions

Let E be a ring of entire functions on with the operation of pointwise multiplication, and let f ₁,...,f _m be a set of nonzero elements in E. The ideal E(f ₁,...,f _m ) in E with generators f ₁,...,f _m is said to be generating if E(f ₁,...,f _m ) = E. The generating ideals in rings of entire functions on determined by the growth of their maximum moduli are characterized in terms of the distribution of the zero sets of their generators. Under the additional condition of rapid variation of the weight sequences determining the ring, criteria for generating ideals are established; they are stated in terms of d(z) max _{1 j m} d _j (z), where d _j (z) is the distance from a point to the zero set of f _j for 1 j m. It is shown that, in rings of entire functions of finite or minimal type with respect to a given order, a similar characterization (i.e., in terms of d(z)) cannot be given.     

On Uncountable Unions and Intersections of Measurable Sets

We consider several natural situations where the union or intersection of an uncountable family of measurable (in various senses) sets with a good additional structure is again measurable or may fail to be measurable. We primarily deal with Lebesgue measurable sets and sets with the Baire property. In particular, uncountable unions of sets homeomorphic to a closed Euclidean simplex are considered in detail, and it is shown that the Lebesgue measure and the Baire property differ essentially in this aspect. Another difference between measure and category is illustrated in the case of some uncountable intersections of sets of full measure (comeager sets, respectively). We also discuss a topological form of the Vitali covering theorem, in connection with the Baire property of uncountable unions of certain sets.     

Decompositions of metrizable compact spaces admittingT-systems of complex-valued functions

Upper semicontinuous decompositions into continua of a metrizable compact space admitting a Chebyshev system of continuous complex-valued functions are considered. It is proved that the cyclic elements of the Moore decomposition space can be embedded in the two-dimensional sphere. Translated fromMatematicheskie Zametki, Vol. 62, No. 2, pp. 259–267, August, 1997. Translated by O. V. Sipacheva     

Limit sets of typical continuous functions

Given a metrizable compact topological n-manifold X with boundary and a finite positive Borel measure μ on X, we prove that for the typical continuous function , it is true that for every point x in a full μ-measure subset of X the limit set ω(f,x) is a Cantor set of Hausdorff dimension zero, f maps ω(f,x) homeomorphically onto itself, each point of ω(f,x) has a dense orbit in ω(f,x) and f is non-sensitive at each point of ω(f,x); moreover, the function x→ω(f,x) is continuous μ-almost everywhere.     

Three kinds of generalized convexity

This paper gives some properties of quasiconvex, strictly quasiconvex, and strongly quasiconvex functions. Relationships between them are discussed.This research was supported in part by the National Natural Science Foundation of China. The author would like to thank Professor M. Avriel for valuable comments about this paper.