∀ {Ω : Type u_1} {E : Type u_2} {ι : Type u_3} [inst : Preorder ι] {m0 : MeasurableSpace Ω}
  {μ : MeasureTheory.Measure Ω} [inst_1 : NormedAddCommGroup E] [inst_2 : NormedSpace ℝ E] [inst_3 : CompleteSpace E]
  {f g : ι → Ω → E} {ℱ : MeasureTheory.Filtration ι m0} [inst_4 : Preorder E] [AddLeftMono E],
  MeasureTheory.Supermartingale f ℱ μ → MeasureTheory.Martingale g ℱ μ → MeasureTheory.Supermartingale (f + g) ℱ μ