Fix symbol in grammar; this should fix some hyperlinking in the HTML
version.
diff --git a/Doc/ref/ref6.tex b/Doc/ref/ref6.tex
index a476578..ba9c182 100644
--- a/Doc/ref/ref6.tex
+++ b/Doc/ref/ref6.tex
@@ -62,7 +62,7 @@
 debugging assertions\indexii{debugging}{assertions} into a program:
 
 \begin{productionlist}
-  \production{assert_statement}
+  \production{assert_stmt}
              {"assert" \token{expression} ["," \token{expression}]}
 \end{productionlist}