split
α : Type u_1
p✝¹ : α → Prop
inst✝² : DecidablePred p✝¹
p✝ : α → Prop
inst✝¹ : DecidablePred p✝
p : α → Prop
inst✝ : DecidablePred p
x : α
xs : List α
h : p x
i : (List.sublist p xs).Index
⊢ (match ⋯ ▸ ⋯ ▸ i.tail with
    | head => head
    | i.tail => (unsublist p i).tail) =
    (unsublist p i).tail
case h_1
α : Type u_1
p✝¹ : α → Prop
inst✝² : DecidablePred p✝¹
p✝ : α → Prop
inst✝¹ : DecidablePred p✝
p : α → Prop
inst✝ : DecidablePred p
x : α
xs : List α
h : p x
i : (List.sublist p xs).Index
x✝ : (⟨x, ⋯⟩ :: List.sublist p xs).Index
heq✝ : ⋯ ▸ ⋯ ▸ i.tail = head
⊢ head = (unsublist p i).tail

case h_2
α : Type u_1
p✝¹ : α → Prop
inst✝² : DecidablePred p✝¹
p✝ : α → Prop
inst✝¹ : DecidablePred p✝
p : α → Prop
inst✝ : DecidablePred p
x : α
xs : List α
h : p x
i : (List.sublist p xs).Index
x✝ : (⟨x, ⋯⟩ :: List.sublist p xs).Index
i✝ : (List.sublist p xs).Index
heq✝ : ⋯ ▸ ⋯ ▸ i.tail = i✝.tail
⊢ (unsublist p i✝).tail = (unsublist p i).tail