In this scheme the ecash notes don't represent IOUs, the spent ecash notes represent the liability of the User towards the Mint
Bitcoin denominated ecash credit secured by publicly arbitrated escrow providing symmetric trust/incentive relationship between Mint and User. Works similar to a credit card top-up scheme. Instead of depositing bitcoin to the Mint to get ecash issued, the Mint issues credit in the form of ecash. The spent ecash tokens represent the User's liability towards the Mint. The User must periodically provide proof of the unspent balance (turning in expired tokens, which can no longer be spent) and