The patent holder must prove by a preponderance of the evidence—that it is more likely than not—that the defendant either directly infringed a claim of the patent, contributed to another’s infringement, or induced another to infringe. In a district court case, the patent holder must also prove the amount of damages that should be assessed for the infringement. To prove direct infringement, the patent holder must prove that the defendant made, used, sold, offered for sale or imported the claimed invention. Direct infringement may occur literally, meaning that a claim of the patent, when compared to the accused device or process, is an exact match. Alternatively, under a theory known as the doctrine of equivalents, infringement may be found where an element of the accused device, while not literally identical to what is described in a claim of the patent, is interchangeable with what is claimed. An accused product or process infringes under the doctrine of equivalents if the equivalent element does the same work in substantially the same way to accomplish substantially the same result as the patented product or process. This doctrine prevents would-be infringers from avoiding liability by making only trivial changes to their product. Contributory infringement arises where a defendant supplies only a portion of the infringing product or process. To establish liability for contributory infringement, the patent holder must prove that the defendant sold, offered for sale, imported or exported a component that is a material part of a patented invention, and that the defendant knew that the component was especially made or adapted for use in the infringing product. An exception is made for sale of “staple” products—those that have a substantial noninfringing use or uses. To prove inducement, the patent holder must prove that the defendant actively induced another to directly infringe the patent holder’s patent. This requires that the defendant knew of the patent.