 Phan Minh Dung (Dung 1995) initiated a new and fruitful approach to defeasible reasoning, one that focuses on the structure of arguments. Dung defines an argument structure as an ordered pair \( ⟨ A, B ⟩ \), in which \(A\) is a set of arguments and \(B\) is a binary relation on \(A\), representing the attacks relation. In other words, if \( ⟨ x, y ⟩ \in B\), then argument \(x\) is representing as attacking argument \(y\) in some way. An argument is a sequence of propositions, with the last proposition designated as its conclusion. (The premises of an argument can be null, in which case we can treat the argument as equivalent to the assertion of the single proposition it contains.) 