∀ {X Y Z : SSet} {A : X.Subcomplex} {B : Y.Subcomplex} {φ : A.toSSet ⟶ B.toSSet} {C : Z.Subcomplex}
  {ψ : B.toSSet ⟶ C.toSSet} {f' g' : SSet.RelativeMorphism B C ψ} (h : f'.Homotopy g') (f : SSet.RelativeMorphism A B φ)
  {φψ : A.toSSet ⟶ C.toSSet} (fac : CategoryTheory.CategoryStruct.comp φ ψ = φψ),
  CategoryTheory.CategoryStruct.comp SSet.ι₁
      (CategoryTheory.CategoryStruct.comp
        (CategoryTheory.MonoidalCategoryStruct.whiskerRight f.map (SSet.stdSimplex.obj (SimplexCategory.mk 1))) h.h) =
    (f.comp g' fac).map