in_wl_tree
if (in_wl_tree(e, &ubi->used)) {
} else if (in_wl_tree(e, &ubi->scrub)) {
} else if (in_wl_tree(e, &ubi->erroneous)) {
if (e == ubi->move_from || in_wl_tree(e, &ubi->scrub) ||
in_wl_tree(e, &ubi->erroneous)) {
if (in_wl_tree(e, &ubi->used)) {
if (in_wl_tree(e, &ubi->scrub))
else if (in_wl_tree(e, &ubi->erroneous))
} else if (in_wl_tree(e, &ubi->used)) {
} else if (in_wl_tree(e, &ubi->free)) {
if (in_wl_tree(e, root))