Of the several varieties of post-grant challenges created by the Leahy-Smith Americas Invent Act (AIA), challenges under inter partes review (IPR) are characterized by the requirement that they be based only on patents and printed publications. See 35 U.S.C. § 311(b). By contrast, in other proceedings such as post grant reviews, the challenge may rely on any form of prior art or any basis for invalidity, including public prior use.