Minor grammatical fix
diff --git a/Doc/lib/libstring.tex b/Doc/lib/libstring.tex
index 5a0a41c..b04dbbe 100644
--- a/Doc/lib/libstring.tex
+++ b/Doc/lib/libstring.tex
@@ -142,7 +142,7 @@
Return the number of (non-overlapping) occurrences of substring
\var{sub} in string \code{\var{s}[\var{start}:\var{end}]}.
Defaults for \var{start} and \var{end} and interpretation of
- negative values is the same as for slices.
+ negative values are the same as for slices.
\end{funcdesc}
\begin{funcdesc}{lower}{s}