(1) A ticket shall be deemed to have been issued subject to the condition of availability of accommodation in the class of carriage and the train for which the ticket is issued.
     (2) If no accommodation is available in the class of carriage for which a ticket is issued, and the holder thereof travels in a carriage of a lower class, he shall, on returning such ticket, be entitled to a refund of the difference between the fare paid by him and the fare payable for the class of carriage in which he travels.