Sub-posets in ${\omega }^{\omega }$ and the Strong Pytkeev${}^{\ast }$ 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.