AST translation rules no longer require constant head on LHS;

--- a/doc-src/Ref/syntax.tex	Sun Jul 16 20:46:44 2000 +0200
+++ b/doc-src/Ref/syntax.tex	Sun Jul 16 20:47:15 2000 +0200
@@ -422,9 +422,6 @@
 \begin{itemize}
 \item Rules must be left linear: $l$ must not contain repeated variables.
 
-\item Rules must have constant heads, namely $l = \mtt"c\mtt"$ or $l =
-  (\mtt"c\mtt" ~ x@1 \ldots x@n)$.
-
 \item Every variable in~$r$ must also occur in~$l$.
 \end{itemize}