As interpreted by the Patent and Trademark Office (PTO), to be "novel" an invention must not have been known and available to the public at the time of the application. "Utility" refers to usefulness. To qualify, a proposed patent must specify a concrete function, service, or purpose. According to the criteria of "non-obviousness" an invention cannot obtain a patent if the differences between its specific subject matter and the prior art are such that "the subject matter as a whole would have been obvious at the time the invention was made to a person having ordinary skill in the art to which said subject matter pertains" (35 United States Code, Sec. 103).