To decide whether an inventor is violating (infringing) a patent, it is necessary to carefully examine the patent's "claims." (Claims are terse statements of the scope of the invention, and most patents contain more than one of them.) The elements of each claim must be compared with the elements of the accused infringer's invention (usually a device or process). If the elements of a patent claim match the elements of the device or process (called "reading on" or "teaching" the device or process), an infringement has occurred. Even if the claims don't literally match the elements of the infringing device, it is possible that a court would find an infringement by applying what's known as the "doctrine of equivalents"; that is, the patented invention and the allegedly infringing device or process are sufficiently equivalent in what they do and how they do it to warrant a finding of infringement.