ext_can_merge
if (left && ext_can_merge(left, be)) {
if (right && ext_can_merge(be, right)) {
if (merge_ok && ext_can_merge(new, be)) {
if (merge_ok && ext_can_merge(be, new)) {
if (left && ext_can_merge(left, be)) {
if (right && ext_can_merge(be, right)) {