Make the grammar more consistent, and explain rewrite based on feedback.

chapters/syntax.tex

@@ -258,6 +258,7 @@ \subsection{Modification}\label{modification}
 
 
 \subsection{Equations}\label{equations1}
+See below for how to rewrite rules \lstinline[language=grammar]!equation-or-procedure! and \lstinline[language=grammar]!statement-or-procedure! for recursive descent parsers.
 
 \begin{lstlisting}[language=grammar]
 equation-section :
@@ -267,17 +268,20 @@ \subsection{Equations}\label{equations1}
    [ initial ] algorithm { statement ";" }
 
 some-equation :
-   ( simple-expression "=" expression
+   ( equation-or-procedure
      | if-equation
      | for-equation
      | connect-equation
      | when-equation
-     | component-reference function-call-args
    )
    description
 
+equation-or-procedure :
+  simple-expression "=" expression
+  | component-reference function-call-args
+
 statement :
-   ( component-reference ( ":=" expression | function-call-args )
+   ( statement-or-procedure
      | "(" output-expression-list ")" ":="
        component-reference function-call-args
      | break
@@ -289,6 +293,10 @@ \subsection{Equations}\label{equations1}
    )
    description
 
+statement-or-procedure :
+  component-reference ":=" expression
+  | component-reference function-call-args
+
 if-equation :
    if expression then
      { some-equation ";" }
@@ -352,6 +360,12 @@ \subsection{Equations}\label{equations1}
    connect "(" component-reference "," component-reference ")"
 \end{lstlisting}
 
+\begin{nonnormative}
+The productions \lstinline[language=grammar]!equation-or-procedure! and \lstinline[language=grammar]!statement-or-procedure! are not suitable for recursive descent parsers.
+
+A work-around is to left-factor them and for \lstinline[language=grammar]!equation-or-procedure! introduce semantic checks to ensure that only the grammar above is accepted.
+\end{nonnormative}
+
 \subsection{Expressions}\label{expressions1}
 
 \begin{lstlisting}[language=grammar]