Merge pull request modelica#3555 from HansOlsson/ImproveText

AsSuggested

chapters/classes.tex

@@ -620,7 +620,7 @@ \subsection{Discrete-Time Variables}\label{discrete-time-variables}
 Note that this is not the same as saying that \lstinline!der(vd) = 0! almost everywhere, as the derivative is not even defined at the events.
 It is not allowed to apply \lstinline!der! to discrete-time variables.
 
-If a \lstinline!Real! variable is declared with the prefix \lstinline!discrete!\indexinline{discrete} it must in a simulation model be assigned in a \lstinline!when!-clause, either by an assignment or an equation.
+If a \lstinline!Real! variable in a simulation model is declared with the prefix \lstinline!discrete!\indexinline{discrete}, it must be assigned in a \lstinline!when!-clause, either by an assignment or an equation.
 The variable assigned in a \lstinline!when!-clause shall not be defined in a sub-component of \lstinline!model! or \lstinline!block! specialized class.
 (This is to keep the property of balanced models.)