Simple Contrapositive Assumption-Based Frameworks

We study the Dung semantics for extended forms of assumptionbased argumentation frameworks (ABFs), based on any contrapositive propositional logic, and whose defeasible rules are expressed by arbitrary formulas in that logic. New results on the well-founded semantics for such ABFs are reported, the redundancy of the closure condition is shown, and the use of disjunctive attacks is investigated. Useful properties of the generalized frameworks are also considered.