A sync-ordered multicast operation is one whose delivery ordering semantics are the same as those
for delivering views in a view-synchronous group communication system. In a thingumajig
service, operations upon thingumajigs are causally ordered. The service supports lists of users able
to perform operations on each particular thingumajig. Explain why removing a user from a list
should be a sync-ordered operation.

What will be an ideal response?

Sync-ordering the remove-user update ensures that all processes handle the same set of operations on a
thingumajig before the user is removed. If removal were only causally ordered, there would not be any definite
delivery ordering between that operation and any other on the thingumajig. Two processes might receive an
operation from that user respectively before and after the user was removed, so that one process would reject
the operation and the other would not.