An inventive entity cannot obtain claims in two patents directed either to the same invention or to an obvious variation of the same invention. Where the inventions are identical, the second patent is invalid. With respect to obvious variations, this rejection can be overcome by filing a terminal disclaimer that, in effect, states that the second or any additional patents to issue will expire on the same date as the first patent, thereby eliminating any improper extension of the period of exclusivity resulting from the second or additional patents. A challenge based upon double patenting cannot be made where a second patent has issued as a result of a U. S. Patent and Trademark Office restriction requirement and the filing of a divisional application. In such a situation, the only reason more than one patent was issued is that the U. S. Patent and Trademark Office compelled limitation of a prior case to one embodiment.