simp [List.all, List.foldr] at all
α : Type u_1
p : α → Bool
iv : Nat
h : α
t : List α
all : List.all (h :: t) p = true
ilt : iv < List.length (h :: t)
⊢ p (List.get (h :: t) { val := iv, isLt := ilt }) = true
α : Type u_1
p : α → Bool
iv : Nat
h : α
t : List α
ilt : iv < List.length (h :: t)
all : p h = true ∧ List.foldr (fun a r => p a && r) true t = true
⊢ p (List.get (h :: t) { val := iv, isLt := ilt }) = true