fact: Definition opcartesian_to_invertible : is_invertible_2cell (α ▹ π₂).
imports: UniMath.Foundations.All UniMath.MoreFoundations.All UniMath.CategoryTheory.Core.Categories UniMath.Bicategories.Core.Bicat UniMath.Bicategories.Core.Invertible_2cells UniMath.Bicategories.Morphisms.InternalStreetFibration UniMath.Bicategories.Morphisms.InternalStreetOpFibration UniMath.Bicategories.Limits.Products