ction because the balance in one account is reduced and the
balance in the other increases. If the reduction happened before the
increase, than a poorly-timed system crash could leave the customer
poorer; if the bank used the opposite order, then the same system crash
could make the customer richer. Obviously, both the customer and the
bank are best served if both operations happen at the same instant.</p>
        <p>Transactions have well-defined properties in database systems. They are
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