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Multiplicative finite embeddability vs divisibility of ultrafilters. (English) Zbl 07541622

This article is part of the author’s work to investigate the divisibility in \(\beta \mathbb{N}\) in recent years. In this paper the author investigates the exploration of various aspects of divisibility of ultrafilters. By several ways the divisibility relation \(|\) on the natural numbers \(\mathbb{N}\) has been extended from the natural numbers to \(\beta\mathbb{N}\). Now \((\beta \mathbb{N},\cdot)\) is non-commutative, so naturally we will have three types of divisibility of ultrafilters as left \((|_L)\), right \((|_R)\) and middle \((|_M)\) divisibility. A stronger divisibility \(\widetilde{|}\) can also be defined on \(\beta \mathbb{N}\) and the notion multiplicative finite embeddability \(\leq_{fe}\) be introduced.
It is proved that \(|_L\subset \leq_{fe}\subset \tilde{|}\) and \(|_M\subset C\subset \tilde{|}\). In Section 3, the reader can find some relations between \(\leq_{fe}\)-minimal elements, prime ultrafilters and \(\mathbb{N}\)-free ultrafilters. In Section 4, the \(\tilde{|}\)-greatest class has been denoted by MAX. It is proved that MAX is a \(\cdot\)-ideal and \(+\)-closed in \(\beta\mathbb{N}\). In particular, the closure of additive idempotents is a subset of MAX. In Section 5, the reader can find a new version of classification of large sets. Finally, in Section 6 the reader can find some open problems.

MSC:

54D35 Extensions of spaces (compactifications, supercompactifications, completions, etc.)
54D80 Special constructions of topological spaces (spaces of ultrafilters, etc.)
11U99 Connections of number theory and logic
03E05 Other combinatorial set theory
03H15 Nonstandard models of arithmetic

References:

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