Five on Nostr: Thanks for the article! Can you elaborate on the DLEQ proof? How it works and why it ...

Thanks for the article!
Can you elaborate on the DLEQ proof?
How it works and why it is important?
I think that nip61 nutzaps don't yet use this but it is still considered only spendable by the receiver.

So it boils down to this question:
If I received a nutzap offline and trusted the mint, but there is no DLEQ, is that not final settlement yet?