ITF_USED
#define ITF_MASK (ITF_INSERTED|ITF_USED)
if (it == NULL || it->it_flags & ITF_USED)
it->it_flags |= ITF_USED;
if (it->it_flags & ITF_USED)
old->it_flags &= ~ITF_USED;
} else if (it->it_flags & ITF_USED) {
if (it->it_flags & ITF_USED) {