public void deleteAppointment(Appointment st)
{
var original = Appointments.Find(a => a.AppointmentID == st.AppointmentID);
if (original != null && Encoding.ASCII.GetString(original.timestamp) == Encoding.ASCII.GetString(st.timestamp))
{
var at = Attendances.First(a => a.AppointmentID == st.AppointmentID);
Attendances.Remove(at);
}
else
{
throw new Exception("Your appointment version is not actualy");
}
}
