∀ {α : Type u_1} {β : Type u_2} [inst : LinearOrder β] {f : α → β} [inst_1 : DecidableEq α] {l : List α} {m : α},
  m ∈ List.argmax f l → ∀ {a : α}, a ∈ l → f m ≤ f a → List.idxOf m l ≤ List.idxOf a l