  The development and testing of applications, such as the problem of formalizing the reasoning involved in getting to the airport, posed as a challenge in  McCarthy 1959  (see  Section 2.2,  below), doesn’t even appear as a category in the list of JPL topics, and in fact most of the philosophical logic literature is theoretical in nature, and is tested using philosophical techniques. Essentially, this means that the theories are motivated and tested with small-scale, artificial examples, selected by the theoreticians. These examples usually serve more as demonstrations or illustrations than as tests.