+void btr_merge(struct btr_node *btrn, size_t dest_size);
+bool btr_eof(struct btr_node *btrn);
+void btr_log_tree(struct btr_node *btrn, int loglevel);
+int btr_pushdown_one(struct btr_node *btrn);
+bool btr_inplace_ok(struct btr_node *btrn);
+int btr_node_status(struct btr_node *btrn, size_t min_iqs,
+ enum btr_node_type type);