fix typo (#1030)

doc/attr.xml

@@ -1292,7 +1292,7 @@ true]]></Example>
 
     <C>NambooripadPartialOrder</C> returns the Nambooripad partial order on the
     regular semigroup <A>S</A> as a list of sets of positive integers where
-    entry <C>i</C> in <C>NaturalPartialOrder(<A>S</A>)</C> is the set of
+    entry <C>i</C> in <C>NambooripadPartialOrder(<A>S</A>)</C> is the set of
     positions in <C>Elements(<A>S</A>)</C> of elements which are less than
     <C>Elements(<A>S</A>)[i]</C>. See also <Ref
       Func="NambooripadLeqRegularSemigroup"/>.