∀ {C : Type u₁} [inst : CategoryTheory.Category.{v₁, u₁} C] [inst_1 : CategoryTheory.Preadditive C] {D : Type u_1}
  [inst_2 : CategoryTheory.Category.{v₁, u_1} D] [inst_3 : CategoryTheory.Preadditive D] {E : Type u_2}
  [inst_4 : CategoryTheory.Category.{v₁, u_2} E] [inst_5 : CategoryTheory.Preadditive E]
  (F : CategoryTheory.Functor C D) [inst_6 : F.Additive] (G : CategoryTheory.Functor D E) [inst_7 : G.Additive]
  (X : CategoryTheory.Mat_ C), (F.mapMatComp G).inv.app X = CategoryTheory.CategoryStruct.id ((F.comp G).mapMat_.obj X)