Remove extra verb; reported by Detlef Lannert.

Doc/lib/libre.tex

@@ -303,8 +303,7 @@ is not preceded by a match for \regexp{...}.  This is called a
 \dfn{negative lookbehind assertion}.  Similar to positive lookbehind
 assertions, the contained pattern must only match strings of some
 fixed length.  Patterns which start with negative lookbehind
-assertions will may match at the beginning of the string being
-searched.
+assertions may match at the beginning of the string being searched.
 
 \end{list}