   You can see from this that the formulation of the problem presupposes a distinction between direct consequences of actions (ones that attach directly to an action, and that are ensured by the successful performance of the action) and other consequences. This assumption is generally accepted without question in the AI literature on action formalisms. You can make a good case for its common sense plausibility—for instance, many of our words for actions (‘to warm’, to ‘lengthen’, ‘to ensure’) are derived from the effects that are conventionally associated with them. And in these cases, success is entailed: if someone has warmed something, this entails that it became warm. [32] A typical example is discussed in  Lin 1995: a certain suitcase has two locks, and is open if and only if both locks are open. Then (assuming that actions are not performed concurrently) opening one lock will open the suitcase if and only if the other lock is open. Here, opening a lock is an action, with direct consequences; opening a suitcase is not an action, it is an indirect effect.