Free Version
Moderate

# Counting Relatively Compact Subsets

TOPO-NELYVY

Let $X=(\mathbb{Z},\tau)$ be a topological space, where the topology $\tau$ is generated by $\{(n,0,1):n\in\mathbb{Z}, n\not=0,1\}$ and $\{1\}$. Let $Y=\{-1,0,1,2\}\subset X$.