Not all concurrent executions result in a correct state. To illustrate, consider
the schedule of Figure 14.5. After the execution of this schedule, we arrive at a
state where the final values of accounts A and B are $950 and $2100, respectively.
This final state is an inconsistent state, since we have gained $50 in the process of
the concurrent execution. Indeed, the sum A + B is not preserved by the execution
of the two transactions.