Introduction

You have BTC
      ↓
Deposit to your vault (still on Bitcoin!)
      ↓
Get vSAT (your BTC receipt)
      ↓
Use DeFi, swap, create tokens
      ↓
Withdraw anytime → Get your BTC back

// That's all you need for a basic token
static BALANCES: Mapping<Address, U256> = Mapping::new(b"bal");

nexus_fn! {
    fn transfer(to: Address, amount: U256) {
        let sender = Blockchain::msg.sender();
        let sender_bal = BALANCES.get(&sender);
        
        require!(sender_bal >= amount, "Not enough tokens");
        
        BALANCES.set(&sender, sender_bal.sub(amount));
        BALANCES.set(&to, BALANCES.get(&to).add(amount));
    }
}