∀ {T : Type u₁} [inst : CategoryTheory.Category.{v₁, u₁} T] {D : Type u₂} [inst_1 : CategoryTheory.Category.{v₂, u₂} D]
  {C : Type u₃} [inst_2 : CategoryTheory.Category.{v₃, u₃} C] (F : CategoryTheory.Functor C T)
  (G : CategoryTheory.Functor D T) (c : C) (X : CategoryTheory.CostructuredArrow (CategoryTheory.Comma.fst F G) c),
  ((CategoryTheory.CostructuredArrow.ofCommaFstEquivalenceFunctor F G c).obj X).left = CategoryTheory.Over.mk X.hom