  Two results are presented concerning the entailment problem in Separation
Logic with inductively defined predicate symbols and theory reasoning. First,
we show that the entailment problem is undecidable for rules with bounded
tree-width, if theory reasoning is considered. The result holds for a wide
class of theories, even with a very low expressive power. For instance it
applies to the natural numbers with the successor function, or with the usual
order. Second, we show that every entailment problem can be reduced to an
entailment problem containing no equality (neither in the formulas nor in the
recursive rules defining the semantics of the predicate symbols).
