Countable spaces, realcompactness, and the pseudointersection number

Claudio Agostini, Andrea Medini, Lyubomyr Zdomskyy

All spaces are assumed to be Tychonoff. Given a realcompact space $X$, we denote by $\mathsf{Exp}(X)$ the smallest infinite cardinal $\kappa$ such that $X$ is homeomorphic to a closed s…