  For explicitness, let’s use Reiter’s default logic to illustrate the formalization. Recall that in Reiter’s theory, defaults are represented as rules, not formulas, so that they are not subject to quantification. To formalize inertia, then, we need to use default rule schemata. For each fluent f, action a, and situation s, the set of these schemata will include an instance of the following schema: