The bank has three accounts. Each change to a balance adds a row to account_log, with the number of its transaction in tx.

1. Add 5 to Sofia's balance (account 3) with one UPDATE and no BEGIN. Run the same UPDATE a second time.
2. Look at account_log. Do the two new rows have the same tx?
3. Move 100 from Ava (account 1) to Liam (account 2) in one transaction. Do not commit yet. Look at both tabs.
4. Commit the transfer.

If a balance goes wrong, reset the lab and start again.