On March 22, 2010, the U.S. Court of Appeals for the Federal Circuit reaffirmed its rule that every patent application include a “written description” of the invention being claimed. The decision was a victory for WLF, which filed a brief supporting the rule. WLF argued that patent law includes a “written description” requirement that is in addition to the requirement that an application include information sufficient “to enable any person skilled in the art” to make and use the invention. The appeals court agreed with WLF that enforcing the “written description” requirement prevents patentees from later amending claims to assert that later-developed products infringe the initial patent. The appeals court recognized that its decision makes it more difficult to patent “basic research” that lacks a practical application. But the court said that Congress intended the patent system to encourage useful inventions, not to grant scientists a proprietary interest in ongoing research.