  Most existing computational tools for assumption-based argumentation (ABA)
focus on so-called flat frameworks, disregarding the more general case. In this
paper, we study an instantiation-based approach for reasoning in possibly
non-flat ABA. We make use of a semantics-preserving translation between ABA and
bipolar argumentation frameworks (BAFs). By utilizing compilability theory, we
establish that the constructed BAFs will in general be of exponential size. In
order to keep the number of arguments and computational cost low, we present
three ways of identifying redundant arguments. Moreover, we identify fragments
of ABA which admit a poly-sized instantiation. We propose two algorithmic
approaches for reasoning in possibly non-flat ABA. The first approach utilizes
the BAF instantiation while the second works directly without constructing
arguments. An empirical evaluation shows that the former outperforms the latter
on many instances, reflecting the lower complexity of BAF reasoning. This
result is in contrast to flat ABA, where direct approaches dominate
instantiation-based approaches.
