global protocol Booking(role C, role A, role S)
{
    rec Loop {
        choice at C
        {
            choice at C
            {
                Yes() from C to A;
                Yes() from A to S;
                Payment(int) from C to S;
                Ack() from S to C;
            }
            or
            {
                No() from C to A;
                No() from A to S;
            }
            Bye() from C to A;
        }
        or
        {
            Query(int) from C to A;
            Quote(int) from A to C;
            Dummy() from A to S;   // Dummy
            continue Loop;
        }
    }
}