On December 24, 2002, anticipating the expiration of exclusive marketing rights, generic drug manufacturers Mylan, Teva, Barr, and Ranbaxy applied to the FDA to market a generic form of modafinil. At least one withdrew its application after early opposition by Cephalon based on the RE 37,516 patent. There is some question of whether a particle size patent is sufficient protection against the manufacture of generics. Pertinent questions include whether modafinil may be modified or manufactured to avoid the granularities specified in the new Cephalon patent, and whether patenting particle size is invalid because particles of appropriate sizes are likely to be obvious to practitioners skilled in the art. However, under United States patent law, a patent is entitled to a legal presumption of validity, meaning that in order to invalidate the patent, much more than "pertinent questions" are required.