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Consider a variant of the tree protocol called the forest protocol. The database is organized as a forest of rooted trees. Each transaction $T_i$ must follow the following rules:
$•$ The first lock in each tree may be on any data item.
$•$ The second, and all subsequent, locks in a tree may be requested only if the parent of the requested node is currently locked.
$•$ Data items may be unlocked at any time.
$•$ A data item may not be relocked by Ti after it has been unlocked by $T_i$.
Show that the forest protocol does not ensure serializability.

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