In United States patent law, utility is a patentability requirement. As provided by , an invention is "useful" if it provides some identifiable benefit and is capable of use and "useless" otherwise. The majority of inventions are usually not challenged as lacking utility, but the doctrine prevents the patenting of fantastic or hypothetical devices such as perpetual motion machines. The patent examiners guidelines require that a patent application expresses a specific, credible, and substantial utility. Rejection by an examiner usually requires documentary evidence establishing a prima facie showing that there is no specific, substantial, and credible utility. European patent law does not consider utility as a patentability criterion. Instead, it requires that to be patentable an invention must have industrial applicability. Utility criteria In considering the requirement of utility for patents, there are three main factors to review: operability of the invention, a beneficial use of the invention, and practical use of the invention. Operability The importance of operability as a requirement of claims is disputed. Janice Mueller claims that an inoperable invention may fail to satisfy the enablement requirement under 35 U.S.C. § 112 because "an inventor cannot properly describe how to use an inoperable invention...." However, as authority Ms. Mueller's textbook cites to another textbook, Landis on Mechanics of Patent Claim Drafting, which itself cites section 2173.05(l) in the Manual of Patent Examining Procedure. Section 2173.05(l) has not been part of the Manual of Patent Examining Procedure since the 1990s. The most recent pronouncement of the Manual of Patent Examining Procedure is 2107.01: Situations where an invention is found to be "inoperative" and therefore lacking in utility are rare, and rejections maintained solely on this ground by a Federal court even rarer. In many of these cases, the utility asserted by the applicant was thought to be "incredible in the light of the knowledge of the art, or factually misleading" when initially considered by the Office. ... Other cases suggest that on initial evaluation, the Office considered the asserted utility to be inconsistent with known scientific principles or "speculative at best" as to whether attributes of the invention necessary to impart the asserted utility were actually present in the invention. ... However cast, the underlying finding by the court in these cases was that, based on the factual record of the case, it was clear that the invention could not and did not work as the inventor claimed