rintro ⟨W,M,w,satX⟩
case mpr
X : Finset Formula
φ : Formula
⊢ Satisfiable (X ∪ {φ}) → Satisfiable (X ∪ {~~φ})
case mpr.intro.intro.intro
X : Finset Formula
φ : Formula
W : Type
M : KripkeModel W
w : W
satX : ∀ φ_1 ∈ X ∪ {φ}, Evaluate (M, w) φ_1
⊢ Satisfiable (X ∪ {~~φ})