{C : Type u} →
  [inst : CategoryTheory.Category.{v, u} C] →
    {J : CategoryTheory.GrothendieckTopology C} →
      [inst_1 : CategoryTheory.HasWeakSheafify J (Type v)] →
        (sq : CategoryTheory.Square C) →
          [CategoryTheory.Mono sq.f₂₄] →
            [CategoryTheory.Mono sq.f₃₄] →
              sq.IsPullback → CategoryTheory.Sieve.ofTwoArrows sq.f₂₄ sq.f₃₄ ∈ J sq.X₄ → J.MayerVietorisSquare