Report Number: CS-TN-94-7
Institution: Stanford University, Department of Computer Science
Title: Overcoming Unexpected Obstacles
Author: McCarthy, John
Date: May 1994
Abstract: The present note illustrates how logical formalizations of common sense knowledge and reasoning can achieve some of the open-endedness of human common sense reasoning. A plan is made to fly from Glasgow to Moscow and is shown by circumscription to lead to the traveller arriving in Moscow. Then a fact about an unexpected obstacle---the traveller losing his ticket---is added without changing any of the previous facts, and the original plan can no longer be shown to work if it must take into account the new fact. However, an altered plan that includes buying a replacement ticket can now be shown to work. The formalism used is a modification of one developed by Vladimir Lifschitz, and I have been informed that the modification isn't correct, and I should go back to Lifschitz's original formalism.