(a) the display of the invention with the consent of the true and first inventor or a person deriving title from him at an industrial or other exhibition to which the provisions of this section have been extended by the Central Government by notification in the Official Gazette, or the use thereof with his consent for the purpose of such an exhibition in the place where it is held; or

(b) the publication of any description of the invention in consequence of the display or use of the invention at any such exhibition as aforesaid; or

(c) the use of the invention, after it has been displayed or used at any such exhibition as aforesaid and during the period of the exhibition, by any person without the consent of the true and first inventor or a person deriving title from him; or

(d) the description of the invention in a paper read by the true and first inventor before a learned society or published with his consent in the transactions of such a society,