⊦ zh = zh0 ↔ (∀ r. (r ∈ zh ↔ r ∈ zh0) ∧ (r ∈ zh → zh[r] = zh0[r]))
∅ = zh0 ∪ zh1, zh0 ⊥ zh1 ⊦ (∀ r. (r ∈ zh0 ↔ r ∈ ∅) ∧ (r ∈ zh0 → zh0[r] = (∅)[r])) ∧ zh1 = ∅
Used terms: ∅, zh0