∀ a. a ∈ s → a ∈ s0 ⊦ (∀ a. a ∈ s0 → a ∈ s) ↔ (∀ a. a ∈ s ↔ a ∈ s0)
Used simplifier rules: Subset: ⊦ s1 ⊆ s2 ↔ (∀ a. a ∈ s1 → a ∈ s2);%Extension: ⊦ s1 = s2 ↔ (∀ a. a ∈ s1 ↔ a ∈ s2);