I Type too fast — got A and B mixed up. Below is the fix:
> That breaks single-copy semantics: A client may have acted on data after
> it had been changed by somebody else. Say, A and B are sharing the file.
> B has a read-lease on the file, A obtains a write lease, modifies the file
> and sends a message to B to read what was changed. B reads the file (which
> is still in the cache and has not been updated). Meanwhile, just after A
> obtained the write lease, the server notifies B that the lease is expiring
> early, but this message travels slowly and doesn't arrive until the whole
> exchange is over.
