Make non-normative statement about root finding more freestanding

Addressing review comment by Hans.

chapters/equations.tex

@@ -594,7 +594,7 @@ \section{Events and Synchronization}\doublelabel{events-and-synchronization}
 has the constant value of the expression from the last event instant.
 
 \begin{nonnormative}
-in other words, a root finding mechanism is needed which determines a small time interval in which the expression changes its value; the event occurs
+A root finding mechanism is needed which determines a small time interval in which the expression changes its value; the event occurs
 at the right side of this interval.
 \end{nonnormative}