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The substance-transformation rule makes a process patent-eligible even though it is not limited to any particular implementing apparatus or device, so long as the process transforms one substance into another (for example, as in the vulcanization of rubber by heating it in the presence of sulfur). The device rule involves the fact that most processes (and other inventions) are based on an underlying scientific principle, phenomenon of nature, or abstract idea (collectively, a principle). The clue to the patent-eligibility of processes that do not involve substance-transformation is whether the process implements its underlying principle nontrivially with a machine or other device specifically adapted to carry out the process. Although the Supreme Court has left open the possibility that a process might be patent-eligible that did not transform one substance into another and that was not implemented in a nontrivial manner with a device specifically designed to carry out the process, no such example has yet been recognized. These clues to patent-eligibility do not, however, fully exhaust the subject. There are at least two other clues to the patent-eligibility of products and processes.