Clean up a sad sentence in the yield description.
diff --git a/Doc/ref/ref6.tex b/Doc/ref/ref6.tex
index bd91c11..1f1486b 100644
--- a/Doc/ref/ref6.tex
+++ b/Doc/ref/ref6.tex
@@ -476,11 +476,11 @@
invoked, the function can proceed exactly as if the \keyword{yield}
statement were just another external call.
-One restriction in the use of the \keyword{yield} statement is is that
-is is not allowed in the try clause of a \keyword{try}
-...\ \keyword{finally} construct. The difficulty is that there's no
-guarantee the generator will ever be resumed, hence no guarantee that
-the \keyword{finally} block will ever get executed.
+The \keyword{yield} statement is not allowed in the \keyword{try}
+clause of a \keyword{try} ...\ \keyword{finally} construct. The
+difficulty is that there's no guarantee the generator will ever be
+resumed, hence no guarantee that the \keyword{finally} block will ever
+get executed.
\begin{seealso}
\seepep{0255}{Simple Generators}