interface account
{
    readonly attribute short balance;
    boolean deposit(in short amount);
    boolean withdraw(in short amount);
};

struct trans
{
    short type;
    account customer;
    short amount;
};

interface bank
{
    exception InvalidTransaction
    {
        trans transaction;
    };

    deferred boolean transaction(in trans transaction)
        raises (InvalidTransaction);
    short lastTransaction();
};