rcases ldiff with ⟨τ, τ_in, disagree⟩
case mpr
α : Program
ℓ ℓ' : TP α
W : Type
M : KripkeModel W
w : W
ldiff : ∃ x, ∃ (x_1 : x ∈ testsOfProgram α), ¬ℓ ⟨x, x_1⟩ = ℓ' ⟨x, x_1⟩
⊢ evaluate M w (signature α ℓ) → ¬evaluate M w (signature α ℓ')
case mpr.intro.intro
α : Program
ℓ ℓ' : TP α
W : Type
M : KripkeModel W
w : W
τ : Formula
τ_in : τ ∈ testsOfProgram α
disagree : ¬ℓ ⟨τ, τ_in⟩ = ℓ' ⟨τ, τ_in⟩
⊢ evaluate M w (signature α ℓ) → ¬evaluate M w (signature α ℓ')