unset

Clear the value tagged with (timestamp, replica) — a last-writer-wins tombstone. It competes under piece exactly like a set: an unset at a later tag hides an earlier value, and a set at a later tag revives the register. After an unset wins, value reads null.

It is a write, not a clear: unsetting an empty register still records (timestamp, replica, null), which is what beats a concurrent earlier set arriving later. Like set it goes through piece and so is inflationary — it refuses to lose, it does not refuse to write.

The tag-uniqueness precondition on set applies equally here: never reuse a (replica, timestamp) pair across writes.