If there is more than one effect of an event e, we write for the time of the main effect, and for the time of the effect of changing f. For instance, flying from Glasgow to London has as its resulting situation the situation where you arrive in London. However, another effect of this event is to no longer have your ticket, as the air-hostess takes it from you. The situation where she takes the ticket off you is picked out by . At this situation, the fluent Has(ticket) is also made false. We use other situations like the time the airline-steward takes your ticket, rather than explicit times, as explicit times, like all numerical values are less natural--the numbers are hard to get. The statement that you no longer have your ticket after the air-hostess takes it is very intuitive, while the statement that your no longer have your ticket after n minutes, for some definition of n is not.