enrich
aubifs-inv
with
functions . [ . ] : node-index × key-set → address-set;
axioms lookup-keys : ⊦ adr ∈ ri[ks] ↔ (∃ key. key ∈ ks ∧ key ∈ ri ∧ adr = ri[key]);
used for: ls;
end enrich