cases i
α : Type u_1
xs : List α
p : α → Bool
i : Fin (List.length xs)
all : List.all xs p = true
⊢ p (List.get xs i) = true
case mk
α : Type u_1
xs : List α
p : α → Bool
all : List.all xs p = true
val✝ : Nat
isLt✝ : val✝ < List.length xs
⊢ p (List.get xs { val := val✝, isLt := isLt✝ }) = true