⊦ n0 ∈ (ns ++ n) \ dom gstore ↔ n0 = n ∨ n0 ∈ ns \ dom gstore, n ∈ gstore
Used simplifier rules: ⊦ n ∈ ns ++ n0 ↔ n = n0 ∨ n ∈ ns; (s)