An inventor is a party who conceived (not just contributed to the reduction-to-practice) at least one claim to a patent. The courts explain that "he threshold question" of inventorship is "who conceived the invention." Courts recognize that invention is rarely a solitary endeavor. Therefore, conception and "intellectual domination" over an invention is important and "reduction to practice, "", is irrelevant. One must contribute to the conception to be an inventor." For example, in 1991, consumer group Public Citizen sued the owners of the patent for use of the anti-retroviral compound AZT against HIV Aids, Burroughs-Wellcome. The plaintiffs claimed that several persons at the National Institutes of Health (NIH) who had contributed to the patentable subject matter were not named as "inventors." Controversially, the courts ultimately ruled that the original patent was valid, and no error had been made in excluding the NIH researchers whose work only 'confirmed' the invention.