global protocol OnlineWallet(role S, role C, role A) {
    login(id: string, pw: string) from C to A;
    choice  at A {
        login_ok () from A to C;
        login_ok () from A to S;
        rec  LOOP {
            account(balance: int, overdraft: int) from S to C;
            choice  at C {  @< amount <= balance+overdraft >
                pay(payee: string, amount: int) from C to S;
                continue  LOOP;
            } or {
                quit() from C to S;
            }
        }
    } or {
        login_fail(error: string) from A to C;
        login_fail(error: string) from A to S;
    }
}