ABA+: Assumption-Based Argumentation with Preferences
  We present ABA+, a new approach to handling preferences in a well known
structured argumentation formalism, Assumption-Based Argumentation (ABA). In
ABA+, preference information given over assumptions is incorporated directly
into the attack relation, thus resulting in attack reversal. ABA+
conservatively extends ABA and exhibits various desirable features regarding
relationship among argumentation semantics as well as preference handling. We
also introduce Weak Contraposition, a principle concerning reasoning with rules
and preferences that relaxes the standard principle of contraposition, while
guaranteeing additional desirable features for ABA+.
