Add a paragraph break

It seems that this should get its own paragraph, for symmetry with nearby paragraphs.

protocol/protocol.tex

@@ -2473,6 +2473,7 @@ $\setof{x \typecolon T \suchthat p_x}$ means the subset of $x$ from $T$
 for which $p_x$ (a boolean expression depending on $x$) holds.
 
 $T \subseteq U$ indicates that $T$ is an inclusive subset or subtype of $U$.
+
 $S \union T$ means the set union of $S$ and $T$.
 
 $S \intersection T$ means the set intersection of $S$ and $T$,