Definition 4.19.3. Let $X$ be a topological space, $f \in C_{c}(X; [0, 1])$ and $U \subset X$ be open, then $f \prec U$ if $\supp{f}\subset U$
Definition 4.19.3. Let $X$ be a topological space, $f \in C_{c}(X; [0, 1])$ and $U \subset X$ be open, then $f \prec U$ if $\supp{f}\subset U$