∀ {T : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} T] {P Q : CategoryTheory.MorphismProperty T} {X : T}
  {A B : P.Over Q X} (f : A.left ≅ B.left),
  CategoryTheory.CategoryStruct.comp f.hom B.hom = A.hom →
    CategoryTheory.CategoryStruct.comp ((CategoryTheory.Functor.id T).map f.hom) B.hom =
      CategoryTheory.CategoryStruct.comp A.hom
        ((CategoryTheory.Functor.fromPUnit X).map (CategoryTheory.Discrete.eqToIso' ⋯).hom)