rfl
W : Type
M : KripkeModel W
w : W
N : ℕ
X : List Formula
XS : List (List Formula)
IH :
  ∀ m < (X :: XS).length,
    ∀ (XS : List (List Formula)), XS.length = m → (evaluate M w (discon XS) ↔ ∃ Y ∈ XS, ∀ f ∈ Y, evaluate M w f)
⊢ XS.length = XS.length
no goals