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A probabilistic ergodic decomposition result

Albert Raugi (2009)

Annales de l'I.H.P. Probabilités et statistiques

Let ( X , 𝔛 , μ ) be a standard probability space. We say that a sub-σ-algebra 𝔅 of 𝔛 decomposes μ in an ergodic way if any regular conditional probability 𝔅 P with respect to 𝔅 andμ satisfies, for μ-almost every x∈X, B 𝔅 , 𝔅 P ( x , B ) { 0 , 1 } . In this case the equality μ ( · ) = X 𝔅 P ( x , · ) μ ( d x ) , gives us an integral decomposition in “ 𝔅 -ergodic” components. For any sub-σ-algebra 𝔅 of 𝔛 , we denote by 𝔅 ¯ the smallest sub-σ-algebra of 𝔛 containing 𝔅 and the collection of all setsAin 𝔛 satisfyingμ(A)=0. We say that 𝔅 isμ-complete if 𝔅 = 𝔅 ¯ . Let { 𝔅 i i I } be a non-empty family...

A problem of Galambos on Engel expansions

Jun Wu (2000)

Acta Arithmetica

1. Introduction. Given x in (0,1], let x = [d₁(x),d₂(x),...] denote the Engel expansion of x, that is, (1) x = 1 / d ( x ) + 1 / ( d ( x ) d ( x ) ) + . . . + 1 / ( d ( x ) d ( x ) . . . d n ( x ) ) + . . . , where d j ( x ) , j 1 is a sequence of positive integers satisfying d₁(x) ≥ 2 and d j + 1 ( x ) d j ( x ) for j ≥ 1. (See [3].) In [3], János Galambos proved that for almost all x ∈ (0,1], (2) l i m n d n 1 / n ( x ) = e . He conjectured ([3], P132) that the Hausdorff dimension of the set where (2) fails is one. In this paper, we prove this conjecture: Theorem. d i m H x ( 0 , 1 ] : ( 2 ) f a i l s = 1 . We use L¹ to denote the one-dimensional Lebesgue measure on (0,1] and d i m H to denote the Hausdorff...

A problem with almost everywhere equality

Piotr Niemiec (2012)

Annales Polonici Mathematici

A topological space Y is said to have (AEEP) if the following condition is satisfied: Whenever (X,) is a measurable space and f,g: X → Y are two measurable functions, then the set Δ(f,g) = x ∈ X: f(x) = g(x) is a member of . It is shown that a metrizable space Y has (AEEP) iff the cardinality of Y is not greater than 2 .

A PU-integral on an abstract metric space

Giuseppa Riccobono (1997)

Mathematica Bohemica

In this paper, we define a -integral, i.e. an integral defined by means of partitions of unity, on a suitable compact metric measure space, whose measure μ is compatible with its topology in the sense that every open set is μ -measurable. We prove that the -integral is equivalent to μ -integral. Moreover, we give an example of a noneuclidean compact metric space such that the above results are true.

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