⊦ n ∈ ns \ ns0 ↔ n ∈ ns ∧ ¬ n ∈ ns0
n0 = n ∨ n0 ∈ ns ∧ ¬ n0 ∈ dom gstore ⊦ n ∈ gstore, (n0 = n ∨ n0 ∈ ns) ∧ ¬ n0 ∈ gstore
Used terms: dom gstore, ns, n0