Admissible sets
Dung studies the attack relation in terms of admissible sets of arguments.
A set of arguments A is admissible if
1. it is conflict-free: There are no arguments ? and ? in A, such that ? attacks ?.
2. the arguments in A are acceptable with respect to A: For any argument ? in A, such that there is an argument ? that attacks ?, there is an argument ? in A that attacks ?.