Nostr + Bitcoin

What does a Nostr public key have in common with a Taproot output's key?

• Both are 20-byte hashes
• Both are 32-byte BIP-340 keys on the secp256k1 curve
• Both are derived from the same seed words

A zap receipt (kind 9735) appears under a note. What does it prove?

• That the sats reached the note's author on-chain
• That the payment can't be refunded
• Only that someone fetched an invoice from the recipient's payment server