... and they gave me a receipt for it. I don't need a receipt for the donut: I'll just give you the money, you give me the donut! End of transaction. We don't need to bring ink and paper into this. I just can't imagine a scenario where I would have to prove I bought a donut. Some skeptical friend: 'Don't even act like I didn't get that donut. I got the documentation right here... oops, it's at home, in the files, under 'D' for donut...'