In a patent or patent application, the claims define, in technical terms, the extent, i.e. the scope, of the protection conferred by a patent, or the protection sought in a patent application. In other words, the purpose of the claims is to define which subject-matter is protected by the patent (or sought to be protected by the patent application). This is termed as the "notice function" of a patent claim—to warn others of what they must not do if they are to avoid infringement liability. The claims are of the utmost importance both during prosecution and litigation alike. For instance, a claim could read: "An apparatus for catching mice, said apparatus comprising a base, a spring member coupled to the base, and ..." "A chemical composition for cleaning windows, said composition substantially consisting of 10–15% ammonia, ..." "Method for computing future life expectancies, said method comprising gathering data including X, Y, Z, analyzing the data, comparing the analyzed data results..." Background In most jurisdictions, a patent is a right to exclude others from making, using, importing, selling or offering for sale the subject matter defined by the claims when the claim is for a thing (apparatus, composition of matter, system, etc.). If a claim is for a method, the right to exclude would be to exclude any single party from carrying out all the steps of the claim. In order to exclude someone from using a patented invention, the patent owner, or patentee, needs to demonstrate in a court proceeding that what the other person is using falls within the scope of a claim of the patent; therefore, it is more valuable to obtain claims that include the minimal set of limitations that differentiate an invention over what came before (i.e., the so-called prior art). But the fewer the limitations in a claim, the more likely it is that the claim will cover, or "read on," what came before and be rejected during examination or found to be invalid at a later time for obviousness or lack of novelty. History Patents have not always contained claims. In many European countries, patents did not contain claims until the 1970s. Before that time, it was often difficult to decide whether a product infringed a patent, since the sole basis to know the extent of protection was the description, in view of the prior art. Claims have been necessary parts of U.S. patent