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