+/* Returns the first node in TOWER. */
+static struct tower_node *
+first_node (const struct tower *t)
+{
+ return abt_to_tower_node_null (abt_first (&t->abt));
+}
+
+/* Returns the first node in TOWER. */
+static struct tower_node *
+last_node (const struct tower *t)
+{
+ return abt_to_tower_node_null (abt_last (&t->abt));
+}
+