http://snsnsnya6h3ot563f3p566wuhfoklkg5f62hokdlaqzcaub3gf4xlxyd.onion/items/42159
But that if each note was tied to a specific public key, then the number of times a note could be transferred would be limited. Whenever you transfer ownership of a UTXO, Mercury Wallet creates a backup transaction in case the Mercury server is uncooperative or offline. This lets the UTXO's current owner cash out of Mercury into their own wallet.