| a1 ∈ s2, a ∈ s2, a ∈ s1, a2 ∈ s1, ∀ a. a ∈ s1 ∨ a ∈ s2 → a ∈ s ⊦ a ∈ s ∧ (a0 ∈ s2 → a0 ∈ s) |
a ∈ s, a1 ∈ s2, a ∈ s2, a ∈ s1, a2 ∈ s1, ∀ a. a ∈ s1 ∨ a ∈ s2 → a ∈ s ⊦ a ∈ s ∧ (a0 ∈ s2 → a0 ∈ s)
a1 ∈ s2, a ∈ s2, a ∈ s1, a2 ∈ s1, ∀ a. a ∈ s1 ∨ a ∈ s2 → a ∈ s ⊦ a ∈ s, a ∈ s ∧ (a0 ∈ s2 → a0 ∈ s)
Used formulas: a ∈ s