Domain

A set of actions is referred to as a domain. Theories (models of the world) we construct are never universal. They are always applicable to some part of the reality only. This part is the domain of the theory. When we apply a theory, we assume that only those actions take place which are within the domain. Make an action which is not included in the domain, and the whole theory may become out of place. The states of the world are defined as subsets of the domain of the theory. Other actions are ignored; they may be either irrelevant, when they have no impact on the legitimacy of the theory, or prohibited, when they make the theory unapplicable.