purposes, as the case may require. (7) An appeal shall lie from any decision of the Registrar under subsection (1), (2), (3), (5) or (6). 19 Prior knowledge or publication of invention excused in certain circumstances (1) A patent shall not be refused or held to be invalid by reason only of the fact that the invention in respect of which the patent is applied for or was granted or any part thereof was published, used or known prior to the effective date of the application if the applicant or the patentee, as the case may be, proves— (a) that the knowledge was acquired or the publication or use was made without his knowledge or consent; and (b) that the knowledge acquired or the matter published or used was derived or obtained from him; and (c) if he learned of the disclosure, use or knowledge before the effective date of his application for the patent, that he applied for and obtained protection for his invention with all reasonable diligence after learning of the disclosure: Provided that the protection afforded by this subsection shall not extend to an applicant for a patent or a patentee who has or whose predecessors in title have commercially worked the invention in Zimbabwe, otherwise than for the purpose of reasonable technical trial thereof, prior to the effective date of the application. (2) The exhibition at an industrial or international exhibition certified as such by the Minister of an invention or the publication subsequently of any description of the invention so exhibited by any person without the privity or consent of the inventor or the reading of a paper by the inventor before a learned society or the publication of such paper shall not prejudice the right of the inventor to apply for or obtain a patent in respect of the invention or the validity of any patent granted on the application if— (a) the application for a patent is made not later than six months from the date of the opening of the exhibition or the reading or publication of that paper, as the case may be; and (b) the inventor has, before exhibiting the invention or reading such paper or permitting such publication, given to the Registrar the prescribed notice of his intention to do so. 20 Provisions for secrecy of certain inventions (1) Where, before or after the appointed day, an application for a patent has been made in respect of an invention and it appears to the Registrar that the invention is one of a class notified to him by the competent authority as relevant for defence purposes, he may give directions for prohibiting or restricting the publication of information with respect to the invention or the communication of such information to any person or class of persons specified in the directions, and while such directions are in force the application may, subject to the directions, proceed up to the acceptance of the complete specification but the acceptance shall not be advertised nor the specification published, and no patent shall be granted in pursuance of the application. (2) Where the Registrar gives any directions in terms of subsection (1), he shall give notice of the application and of the directions to the competent authority and thereupon the following provisions shall have effect, that is to say— (a) the competent authority shall, upon receipt of such notice, consider whether the publication of the invention would be prejudicial to the defence of Zimbabwe and, unless a notice under paragraph (c) has previously been given by the competent authority to the Registrar, shall reconsider that question before the expiration of nine months from the date of lodging of the application for the patent and at least once in every subsequent year; (b) for the purposes of paragraph (a), the competent authority may, at any time after the complete specification has been accepted or, with the consent of the applicant, at any time before the complete specification has been accepted, inspect the application and any documents furnished to the Registrar in connection therewith;