See how \(\mathcal{N}_3\) separates two disjoint closed sets \(A\) and \(B\).
Lemma 3.3: Let \(A, B \subset K\) be disjoint closed sets. For each \(\varepsilon > 0\),
there exists \(H \in \mathcal{N}_3^\sigma\) with \(0 \le H < \varepsilon\) on \(B\) and \(1-\varepsilon < H \le 1\) on \(A\).
The construction iterates Lemma 3.2 over points of \(A\).