Clarify simple function call.

chapters/equations.tex

@@ -59,6 +59,14 @@ \subsection{Simple Equality Equations}\label{simple-equality-equations}
 Also compare with \cref{assignments-from-called-functions-with-multiple-results} about calling functions with multiple outputs in assignment statements.
 \end{nonnormative}
 
+Note that there is also \lstinline!function_name(inexpr1, inexpr2);! which calls the given function or operator.
+It behaves similarly to a simple equation (calling the function or operator), even if it uses a different production in the grammar.
+It is used for special operators like \lstinline!reinit! (\cref{reinit}), \lstinline!assert! (\cref{assert}), and \lstinline!terminate! (\cref{terminate}).
+\begin{nonnormative}
+If the function has any outputs they will be ignored.
+That case is not recommended, but it is allowed to avoid having special rules in function-subtyping \cref{function-compatibility-or-function-subtyping-for-functions}.
+\end{nonnormative}
+
 
 \subsection{For-Equations -- Repetitive Equation Structures}\label{for-equations-repetitive-equation-structures}