 And, as Phan Minh Dung has argued (Dung 1995), formal argumentation can also be used to provide a basis for defining a nonmonotonic consequence relation. A formal argument structure \(F\) is an ordered pair \(⟨A, B⟩\), where \(A\) is a set of arguments, and \(B\) is a binary relation on \(A\) (the attack relation). Then we can say that an argument structure \(F\) has \(p\) has a consequence just in case \(p\) is the conclusion of some argument in the optimal extension of \(F\) (which can be defined in a variety of ways--see section 4.4).