⊦ as = as0 ↔ (∀ adr. adr ∈ as ↔ adr ∈ as0)
key ∈ ri, ri[key] ∈ as, ∀ adr. adr ∈ as ∩ range ri ↔ adr ∈ ∅ ⊦ # as = 0, as = ∅
Used terms: ∅, as ∩ range ri