The purpose of this short note is to give an operator-valued free Poincarè inequality, which provides a simple proof to (an improvement of) a lemma of Voiculescu (2000) asserting that the kernel of the free difference quotient is exactly the coefficients.
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In the present paper, we study bundle convergence in JW- algebra and prove certain ergodic theorems with respect to such convergence. Moreover, conditional expectations of reversible JW-algebras are considered. Using such expectations, the convergence of supermartingales is established.
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Let X and Y be R-valued random variables on a non-atomic probability space (Ω, F, P). We give conditions under which Y can be approximated by a conditional expectation of X. In particular, we prove the following theorem: Let X be an R-valued random variable such that EX+ = EX− = ∞. Then for each random variable Y and arbitrary ϵ > 0 there exist B ∈ F and a sub-σ-field S of F such that P (B) ≤ ϵ and E (X|S) = Y a.s. on Bc. We also review some facts on the conditional expectation of unintegrable random variables.
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Let(Ω,F, P)be a non-atomic probability space. For a given sequence (Xn)of random variables we indicate a number of conditions whichimply that for anyrandom variable Y there exists a sequence(Un) of σ-fields satisfying E(Xn|Un)→Ya.s. In particular, we formulate a sufficient condition using the distributions of Xn’sonly.
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Let (Ω,F, P) be a non-atomic probability space. If (Xn) is a sequence of r.v.’s satisfying Xn → 0 a.s. (respectively, in probability) as n→∞ and EX+n→∞, EX-n→ ∞, as n → ∞, then for any r.v. Y there exists a sequence (Un) of σ-fields such that E(Xn|Un|)→Ya.s. (respectively, in probability) as n→∞.
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Let F and G be distribution functions on R. Then there exist a random variable X and a σ-field U satisfying P(X < a) = F(a), P(E(X|U) < a) = G(a) .[formula]. The consideration is kept on a rather elementary level.
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