Computing defeat statuses

Input: a finite sequence of arguments (the argument stack)  and an attack graph

1. Choose an unmarked argument ? (the first in the stack), if available; otherwise go to 6.

2. If ? is not attacked by any argument or if all arguments attacking ? are marked d (for defeated), then mark ? as u (for undefeated).
3. If ? is attacked by an argument ? that is marked u (for undefeated), then mark ? as d (for defeated).
4. If ? is unmarked, put it at the end of the stack.
5. Go to 1.
6. Stop.