Add new section with references to the implications.

chapters/operatorsandexpressions.tex

@@ -1378,7 +1378,6 @@ \section{Variability of Expressions}\label{variability-of-expressions}
   If \lstinline!v! is a discrete-time component then \lstinline!expr! needs to be a
   discrete-time expression.
 \end{itemize}
-Note that for a function call it is also necessary to consider the variability of any used default arguments, especially if the function is redeclared, see \cref{function-compatibility}.
 
 \begin{example}
 The (underdetermined) model \lstinline!Test! below illustrates two kinds of consequences due to variability constraints.
@@ -1415,6 +1414,10 @@ \section{Variability of Expressions}\label{variability-of-expressions}
 end Test;
 \end{lstlisting}
 \end{example}
+\subsection{Function Variability}\label{function-variability}
+The variability of function calls need to consider both the variability of arguments directly given in the function and the variability of the used default arguments, if any.
+This is especially a concern for functions given as a short class, see \cref{inheritance-of-functions}.
+This has additional implications for redeclarations, see \cref{function-compatibility}.
 
 \subsection{Constant Expressions}\label{constant-expressions}