∀ {T : Type u₁} [inst : CategoryTheory.Category.{v₁, u₁} T] {X : T} (a b c : CategoryTheory.Over X) (f : a ⟶ b)
  (g : b ⟶ c), CategoryTheory.CategoryStruct.comp f.left g.left = (CategoryTheory.CategoryStruct.comp f g).left