∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] {ι : Type w}
  {I : CategoryTheory.Limits.MultispanIndex (CategoryTheory.Limits.MultispanShape.prod ι) C} (self : I.SymmStruct)
  (i j : ι) {Z : C} (h : I.right ((CategoryTheory.Limits.MultispanShape.prod ι).snd (j, i)) ⟶ Z),
  CategoryTheory.CategoryStruct.comp (self.iso i j).hom (CategoryTheory.CategoryStruct.comp (I.snd (j, i)) h) =
    CategoryTheory.CategoryStruct.comp (I.fst (i, j)) h