Reasoning by cases in structured argumentation.
We extend the ASPIC+ framework for structured argumentation so as to allow applications of the reasoning by cases inference scheme for defeasible arguments. Given an argument with conclusion 'A or B', an argument based on A with conclusion C, and an argument based on B with conclusion C, we allow the construction of an argument with conclusion C. Our framework leads to different results than other approaches in non-monotonic logic for dealing with disjunctive information, such as disjunctive default theory or approaches based on the OR-rule (which allows to derive a defeasible rule 'If (A or B) then C', given two defeasible rules 'If A then C' and 'If B then C'). We raise new questions regarding the subtleties of reasoning defeasibly with disjunctive information, and show that its formalization is more intricate than one would presume.