A New Approach to Universal Measurability

Abstract

V. Fedorchuk, A. Chizogidze, and T. Banakh in 2003 and V. Bogachev in 2024 posed the following questions: (i) is it true that $P_τ(X)$ is $C$-embedded in $P_σ(X)$; (ii) Is it true that $P_R(X)$ is $C$-embedded in $P_R(βX)$ if and only if $X$ is pseudocompact, where $P_σ$, $P_τ$, and $P_R$ are the functors of probability $σ$-additive on the Baire $σ$-algebra, $τ$-additive, and Radon measures on the space $X$? The answers to these questions are negative. However, if instead of probability measures we consider the corresponding alternating measures $M_σ$, $M_τ$, and $M_R$, the situation changes. It is proved that (i) $M_τ(X)$ is $C$-embedded in $M_σ(X)$; (ii) $M_R(X)$ is $C$-embedded in $M_R(βX)$ if and only if $X$ is pseudocompact. The question of $C$-embedding of measure spaces is an extension of the question of coincidence of measure spaces, which is a development of the classical concepts of universally measurable and universal measure zero sets. A general theorem is obtained, which leads to the mentioned results.