∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] {D : Type u_1} [inst_1 : CategoryTheory.Category.{v_1, u_1} D]
  [inst_2 : CategoryTheory.Abelian C] [inst_3 : CategoryTheory.HasProjectiveResolutions C]
  [inst_4 : CategoryTheory.Abelian D] {F G H : CategoryTheory.Functor C D} (α : F ⟶ G) (β : G ⟶ H) [inst_5 : F.Additive]
  [inst_6 : G.Additive] [inst_7 : H.Additive],
  CategoryTheory.NatTrans.leftDerivedToHomotopyCategory (CategoryTheory.CategoryStruct.comp α β) =
    CategoryTheory.CategoryStruct.comp (CategoryTheory.NatTrans.leftDerivedToHomotopyCategory α)
      (CategoryTheory.NatTrans.leftDerivedToHomotopyCategory β)