Sub-posets in $\omega^\omega$ and the Strong Pytkeev$^\ast$ Property

TL;DR

This paper explores the structure of posets using Tukey order, constructs a large antichain in $2^\omega$, and investigates the strong Pytkeev$^ extasteriskcentered$ property in topological spaces with $P$-bases, revealing new insights and answering open questions.

Contribution

It establishes the existence of a large antichain of sub-posets in $2^\omega$, links boundedly-complete sub-posets to Tukey quotients, and connects $P$-bases with the strong Pytkeev$^ extasteriskcentered$ property, answering open questions.

Findings

Constructed a $2^\mathfrak{c}$-sized antichain in $2^\omega$ under Tukey order.

Boundedly-complete sub-posets of $\omega^\omega$ are Tukey quotients of $\omega^\omega$.

Spaces with a $P$-base have the strong Pytkeev$^ extasteriskcentered$ property.

Abstract

Tukey order are used to compare the cofinal complexity of partially order sets (posets). We prove that there is a $2^\mathfrak{c}$-sized collection of sub-posets in $2^\omega$ which forms an antichain in the sense of Tukey ordering. Using the fact that any boundedly-complete sub-poset of $\omega^\omega$ is a Tukey quotient of $\omega^\omega$, we answer two open questions published in \cite{FKL16}. The relation between $P$-base and strong Pytkeev$^\ast$ property is investigated. Let $P$ be a poset equipped with a second-countable topology in which every convergent sequence is bounded. Then we prove that any topological space with a $P$-base has the strong Pytkeev$^\ast$ property. Furthermore, we prove that every uncountably-dimensional locally convex space (lcs) with a $P$-base contains an infinite-dimensional metrizable compact subspace. Examples in function spaces are given.