  Accordingly, researchers in logic-based AI have put a lot of effort into developing a variety of non-monotonic reasoning formalisms, such as circumscription (McCarthy 1986), and investigating their application to the frame problem. None of this has turned out to be at all straightforward. One of the most troublesome barriers to progress was highlighted in the so-called Yale shooting problem (Hanks &amp; McDermott 1987), a simple scenario that gives rise to counter-intuitive conclusions if naively represented with a non-monotonic formalism. To make matters worse, a full solution needs to work in the presence of concurrent actions, actions with non-deterministic effects, continuous change, and actions with indirect ramifications. In spite of these subtleties, a number of solutions to the technical frame problem now exist that are adequate for logic-based AI research. Although improvements and extensions continue to be found, it is fair to say that the dust has settled, and that the frame problem, in its technical guise, is more-or-less solved (Shanahan 1997; Lifschitz 2015).