see #3396

doc/expression_concept.htm:

* splitted required methods into to const and non-const methods
* fixed minor typos



[SVN r56006]

libs/numeric/ublas

@@ -1 +1 @@
-Subproject commit 22c1714256ad974c9ea1aaddc8c24f85b2a7c1f7
+Subproject commit 20c1cfd18b3733afa5e212d8c7d42454263e3344