Remove 'an' in "each an event"

chapters/synchronous.tex

@@ -123,7 +123,7 @@ \section{Rationale for Clocked Semantics}\label{rationale-for-clocked-semantics}
   This powerful feature of Modelica to use a nonlinear plant model in a controller would require to export the continuous-time model with an embedded integration method and then import it in an environment where the rest of the controller is defined.
   With clocked equations, clocked controllers with continuous-time models can be directly defined in Modelica.
 \item
-  Clocked equations are straightforward to optimize because they are evaluated exactly once at each an event instant.
+  Clocked equations are straightforward to optimize because they are evaluated exactly once at each event instant.
   In contrast a standard \lstinline!when!-clause with \lstinline!sample! conceptually requires several evaluations of the model (in some cases tools can optimize this to avoid unneeded evaluations).
   The problem for the standard \lstinline!when!-clause is that after \lstinline!v! is changed, \lstinline!pre(v)! shall be updated and the model re-evaluated, since the equations could depend on \lstinline!pre(v)!.
   For clocked equations this iteration can be omitted since \lstinline!previous(v)! can only occur in the clocked equations that are only run the first event iterations.