a ∈ s1, a0 ∈ s1, ∀ a. a ∈ s1 → a ∈ s2 ⊦ a ∈ s2
Used simplifier rules: ⊦ ¬ a ∈ ∅; (s)% ⊦ s1 = s2 ↔ (∀ a. a ∈ s1 ↔ a ∈ s2); (s)%ne-01: ⊦ a ∈ s → s ≠ ∅; (forward) from specification set-basic