  Often, we assume that an action is permitted simply because it is not
explicitly forbidden; or, similarly, that an action is forbidden simply because
it is not explicitly permitted. This kind of assumptions appear, e.g., in
autonomous computing systems where decisions must be taken in the presence of
an incomplete set of norms regulating a particular scenario. Combining default
and deontic reasoning over actions allows us to formally reason about such
assumptions. With this in mind, we propose a logical formalism for default
reasoning over a deontic action logic. The novelty of our approach is twofold.
First, our formalism for default reasoning deals with actions and action
operators, and it is based on the deontic action logic originally proposed by
Segerberg. Second, inspired by Segerberg's approach, we use tools coming from
the theory of Boolean Algebra. These tools allow us to extend Segerberg's
algebraic completeness result to the setting of Default Logics.
