Article 41: Other limitations to patent rights The rights stemming from the patent shall not be extended to: 1° the use of the patented invention on board foreign machines, vessels, vehicles and spacecraft which temporarily or accidentally enter the airspace, waters or territory of the Republic of Rwanda; 2° the acts relating to a patented invention carried out for scientific and technological research purposes and for public non-profit use; 3° the acts performed by any person who, in good faith and on the filing date or, where priority is claimed, on the priority date of the application on the basis of which the patent is granted, was using the invention or was making effective and serious preparations to use it, insofar as these acts do not differ, in their nature or purpose, from previous effective or envisaged use. The right of the prior user referred to in paragraph 1(3) of this article may be transferred or devolve only to the enterprise or business, or part thereof, in which the use or preparations with a view to use took place. It is not an infringement of a patent for any person where the use, manufacture, construction or sale of the patented invention is justified only insofar as it is necessary for the preparation and production of the information file which must be provided according to a domestic or foreign law governing the manufacture, construction, use or sale of a product. Article 42: Duration of the patent and its renewal Subject to the provisions of paragraphs (2), (3) and (4) of this article, the patent shall lapse twenty (20) years after the filing date of the patent application. In order to maintain the patent or patent application in force, an annual fee shall be paid in advance to the empowered authority, for each year, the first being paid one year after the filing date of the patent application. A grace period of six (6) months shall be granted for payment of the annual fee after the deadline, in return for payment of the prescribed surcharge. All fees stipulated in this article shall be determined by a ministerial order. Where an annual fee is not settled in accordance with the provisions of this article, the patent application shall be considered to have been withdrawn or the patent shall lapse.