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Measure and measurable functions of \(S^ n\). (English) Zbl 0876.28004

Summary: Let \(\mathbb{R}\) be the set of real numbers ordered by the usual ordering, \(\widehat{\mathbb{R}}= \mathbb{R}\cup\{-\infty,+\infty\}\) and \(\Xi=\{-,0,+\}\) with \(-<0<+\). The set \(S=\widehat{\mathbb{R}}\times\Xi\backslash \{(-\infty,-),(+\infty,+)\}\) ordered lexicographically and endowed by some partial operations and the order topology, is said to be the quasi-real line and its elements the quasi-real numbers. We clear the disconnected character of \(S\), we give a measure on \(S^n\) and generalize an extension theorem on real-valued functions ranging over a more general than \(S^n\) partially ordered set. The last theorem shows that such a function, under easy conditions, is extended into a continuous function.

MSC:

28A12 Contents, measures, outer measures, capacities
54D35 Extensions of spaces (compactifications, supercompactifications, completions, etc.)
28E99 Miscellaneous topics in measure theory
28A20 Measurable and nonmeasurable functions, sequences of measurable functions, modes of convergence

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