simp
XS YS : List (List Formula)
W : Type
M : KripkeModel W
w : W
⊢ (∃ Y ∈ XS ∪ YS, ∀ f ∈ Y, evaluate M w f) ↔ evaluate M w (discon XS⋁discon YS)
XS YS : List (List Formula)
W : Type
M : KripkeModel W
w : W
⊢ (∃ Y, (Y ∈ XS ∨ Y ∈ YS) ∧ ∀ f ∈ Y, evaluate M w f) ↔ ¬evaluate M w (discon XS) → evaluate M w (discon YS)