{α : Type u_1} →
  {m : MeasurableSpace α} →
    {μ ν : MeasureTheory.Measure α} →
      {motive : μ.HaveLebesgueDecomposition ν → Sort u} →
        ((lebesgue_decomposition : ∃ p, Measurable p.2 ∧ p.1.MutuallySingular ν ∧ μ = p.1 + ν.withDensity p.2) →
            motive ⋯) →
          (t : μ.HaveLebesgueDecomposition ν) → motive t