+inline const_preorder_iterator ex::preorder_begin() const
+{
+ return const_preorder_iterator(*this, nops());
+}
+
+inline const_preorder_iterator ex::preorder_end() const throw()
+{
+ return const_preorder_iterator();
+}
+
+inline const_postorder_iterator ex::postorder_begin() const
+{
+ return const_postorder_iterator(*this, nops());
+}
+
+inline const_postorder_iterator ex::postorder_end() const throw()
+{
+ return const_postorder_iterator();
+}
+