  The leading approaches provide solutions to the main problems mentioned in  Section 4.5,  and to many of the scenarios designed to test and illustrate theories of reasoning about action and change. It is commonly agreed that good solutions need to be generalizable to more complex cases than the early planning formalisms, and that in particular the solutions they offer should be deployable even when continuous time, concurrent actions, and various kinds of ignorance are allowed. Also, it is generally agreed that the formalisms should support several kinds of reasoning, and, in particular, not only prediction and plan verification but retrodiction, i.e., construction of a sequence of states and actions from partial information, presented in narrative form.