Update chapters/classes.tex

Co-authored-by: Henrik Tidefelt <henrikt@wolfram.com>

chapters/classes.tex

@@ -227,7 +227,7 @@ \subsubsection{Prefix Rules}\label{prefix-rules}
 Variables declared with the \lstinline!stream! type prefix shall be a subtype of \lstinline!Real!.
 This is further restricted in \cref{definition-of-stream-connectors}.
 
-Variables declared with the \lstinline!input! type prefix cannot also have the prefix \lstinline!parameter! or \lstinline!constant!.
+Variables declared with the \lstinline!input! type prefix must not also have the prefix \lstinline!parameter! or \lstinline!constant!.
 
 The type prefix \lstinline!flow! of a component that is not a primitive element (see \cref{primitive-elements}), is also applied to the elements of the component (this is done after verifying that the type prefixes occurring on elements of the component are correct).
 Primitive elements with the \lstinline!flow! type prefix shall be a subtype of \lstinline!Real! or an operator record defining an additive group, see \cref{generation-of-connection-equations}.