enrich
node-heap,
tree
with
functions tr : ref × tree → heap → bool;
axioms tr-base : ⊦ tr(r, leaf) = (emp ∧ ⌜r = null⌝ );
used for: s, ls;
tr-rec : ⊦ tr(r, branch(t0, a, t1)) = _∃(λ r0, r1. r => mknode(r0, a, r1) * tr(r0, t0) * tr(r1, t1));
end enrich