| ∀ a. a ∈ s → a ∈ s0, ∀ a. a ∈ s1 → a ∈ s2, a ∈ s ∨ a ∈ s1 ⊦ a ∈ s0, a ∈ s2 |
a ∈ s, ∀ a. a ∈ s → a ∈ s0, ∀ a. a ∈ s1 → a ∈ s2, a ∈ s ∨ a ∈ s1 ⊦ a ∈ s0, a ∈ s2
∀ a. a ∈ s → a ∈ s0, ∀ a. a ∈ s1 → a ∈ s2, a ∈ s ∨ a ∈ s1 ⊦ a ∈ s, a ∈ s0, a ∈ s2
Used formulas: a ∈ s