A.34 Duration and maintenance of patent HARARE Protocol Patents Joint patentees (3) In any proceedings for infringement, the defendant may counter­ claim for the invalidation of the patent and, by way of defence, rely upon any ground on which a patent may be invalidated. (4) The patentee, before instituting proceedings, shall give notice to every licencee to the patent in question whose name is recorded in the patent register, and any such licencee shall be entitled to intervene as co-plaintiff. (5) In any proceedings for infringement, other than criminal proceedings, where the subject matter of the patent is a process for obtaining a product, the burden of establishing that the product was not made by the process shall rest on the defendant if the product obtained by the patented process is new in terms of section 8 (3). (6) In requiring the production of evidence in proceedings for infringement, the court shall take into account the legitimate interests of the defendant in not disclosing his or her manufacturing secrets. (7) The court shall, in awarding damages, calculate such damages taking into account the amount of a reasonable royalty which would have been payable by a licencee or sub-licencee in respect of the patent concerned. (8) The court shall not, in awarding damages under this section, also order, in respect of the same infringement, that the plaintiff be given an account of the profits derived by him or her from the infringement. 28. (1) Subject to subsection (2), a patent shall expire 20 years after the filing date. (2) In order to maintain a patent or patent application, the patentee or the applicant shall pay in advance to the Registrar for each year starting one year after the filing date of the application for the grant of the patent, such annual maintenance fee as may be prescribed. (3) A patent shall lapse or a patent application shall be deemed to have been withdrawn if the owner fails to pay the prescribed fees under subsection (2). (4) Where the patentee or the applicant is late in paying the annual maintenance fee, the Registrar shall, upon the payment of a surcharge that may be prescribed, give the patentee or applicant a grace period of six months, within which to pay the late annual maintenance fee. 29. A patent in respect of which Botswana is a designated State, granted by ARIPO by virtue of the HARARE Protocol, shall have the same effect and enjoy the same protection in Botswana as a patent granted under this Act unless the Registrar communicates, to ARIPO, in respect of the application therefor, a decision, in accordance with the provisions of the Protocol, that if a patent is granted by ARIPO, that patent shall have no effect in Botswana. 30. (1) Where a patent is granted to two or more patentees jointly, the joint patentees shall, in the absence of an agreement to the contrary, be entitled to an equal undivided share in the patent.