Calibres, compacta and diagonals
Paul Gartside, Jeremiah Morgan · Fundamenta Mathematicae · 2015
For a space $Z$ let $\mathcal {K}(Z)$ denote the partially ordered set of all compact subspaces of $Z$ under set inclusion. If $X$ is a compact space, $\Delta $ is the diagonal in $X^2$, and $\mathcal {K}(X^2 \setminus \Delta )$ has calibre $(\omega _1,\o