  We present a labelled sequent calculus for Boolean BI, a classical variant of
O'Hearn and Pym's logic of Bunched Implication. The calculus is simple, sound,
complete, and enjoys cut-elimination. We show that all the structural rules in
our proof system, including those rules that manipulate labels, can be
localised around applications of certain logical rules, thereby localising the
handling of these rules in proof search. Based on this, we demonstrate a free
variable calculus that deals with the structural rules lazily in a constraint
system. A heuristic method to solve the constraints is proposed in the end,
with some experimental results.
