∀ {ι : Type u_1} [inst : Fintype ι] {l : BoxIntegral.IntegrationParams} (I : BoxIntegral.Box ι)
  (π₀ : BoxIntegral.Prepartition I),
  BoxIntegral.IntegrationParams.toFilteriUnion I π₀ = ⨆ c, l.toFilterDistortioniUnion I c π₀