intro XS nDef
W : Type
M : KripkeModel W
w : W
N n : ℕ
IH :
  ∀ m < n, ∀ (XS : List (List Formula)), XS.length = m → (evaluate M w (discon XS) ↔ ∃ Y ∈ XS, ∀ f ∈ Y, evaluate M w f)
⊢ ∀ (XS : List (List Formula)), XS.length = n → (evaluate M w (discon XS) ↔ ∃ Y ∈ XS, ∀ f ∈ Y, evaluate M w f)
W : Type
M : KripkeModel W
w : W
N n : ℕ
IH :
  ∀ m < n, ∀ (XS : List (List Formula)), XS.length = m → (evaluate M w (discon XS) ↔ ∃ Y ∈ XS, ∀ f ∈ Y, evaluate M w f)
XS : List (List Formula)
nDef : XS.length = n
⊢ evaluate M w (discon XS) ↔ ∃ Y ∈ XS, ∀ f ∈ Y, evaluate M w f