+bool
+Grob::pure_is_visible (int start, int end) const
+{
+ return true;
+}
+
+/* Sort grobs according to their starting column. */
+bool
+Grob::less (Grob *g1, Grob *g2)
+{
+ return g1->spanned_rank_interval ()[LEFT] < g2->spanned_rank_interval ()[LEFT];
+}
+