Iosif Petrakis ; Max Zeuner - Pre-measure spaces and pre-integration spaces in predicative Bishop-Cheng measure theory

lmcs:9808 - Logical Methods in Computer Science, October 7, 2024, Volume 20, Issue 4 - https://doi.org/10.46298/lmcs-20(4:2)2024
Pre-measure spaces and pre-integration spaces in predicative Bishop-Cheng measure theoryArticle

Authors: Iosif Petrakis ; Max Zeuner

    Bishop's measure theory (BMT) is an abstraction of the measure theory of a locally compact metric space $X$, and the use of an informal notion of a set-indexed family of complemented subsets is crucial to its predicative character. The more general Bishop-Cheng measure theory (BCMT) is a constructive version of the classical Daniell approach to measure and integration, and highly impredicative, as many of its fundamental notions, such as the integration space of $p$-integrable functions $L^p$, rely on quantification over proper classes (from the constructive point of view). In this paper we introduce the notions of a pre-measure and pre-integration space, a predicative variation of the Bishop-Cheng notion of a measure space and of an integration space, respectively. Working within Bishop Set Theory (BST), and using the theory of set-indexed families of complemented subsets and set-indexed families of real-valued partial functions within BST, we apply the implicit, predicative spirit of BMT to BCMT. As a first example, we present the pre-measure space of complemented detachable subsets of a set $X$ with the Dirac-measure, concentrated at a single point. Furthermore, we translate in our predicative framework the non-trivial, Bishop-Cheng construction of an integration space from a given measure space, showing that a pre-measure space induces the pre-integration space of simple functions associated to it. Finally, a predicative construction of the canonically integrable functions $L^1$, as the completion of an integration space, is included.


    Volume: Volume 20, Issue 4
    Published on: October 7, 2024
    Accepted on: June 26, 2024
    Submitted on: July 19, 2022
    Keywords: Mathematics - Logic,Mathematics - Functional Analysis

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