cases i
α : Type u_1
L1 L2 : List α
i : Fin L1.length
j : Fin L2.length
⊢ L1 = L2 → ↑i = ↑j → L1.get i = L2.get j
case mk
α : Type u_1
L1 L2 : List α
j : Fin L2.length
val✝ : ℕ
isLt✝ : val✝ < L1.length
⊢ L1 = L2 → ↑⟨val✝, isLt✝⟩ = ↑j → L1.get ⟨val✝, isLt✝⟩ = L2.get j