∀ {α : Type u_1} {β : Type u_2} [inst : Mul α] [inst_1 : Preorder α] [inst_2 : Preorder β] {s : Set β}
  [MulLeftStrictMono α] [MulRightMono α] {f g : β → α},
  MonotoneOn f s → StrictMonoOn g s → StrictMonoOn (fun x => f x * g x) s