∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] {J : CategoryTheory.GrothendieckTopology C} {S : C}
  {E F : J.OneHypercover S} (f : E.toPreOneHypercover ≅ F.toPreOneHypercover),
  (CategoryTheory.GrothendieckTopology.OneHypercover.isoMk f).inv = f.inv