-- Mathlib/MeasureTheory/Decomposition/Lebesgue.lean
theorem rnDeriv_smul_right_of_ne_top (ν μ : Measure α) [IsFiniteMeasure ν]
    [ν.HaveLebesgueDecomposition μ] {r : ℝ≥0∞} (hr : r ≠ 0) (hr_ne_top : r ≠ ∞) :
    ν.rnDeriv (r • μ) =ᵐ[μ] r⁻¹ • ν.rnDeriv μ

Proof state:
α : Type u_1
m : MeasurableSpace α
ν μ : Measure α
inst✝¹ : IsFiniteMeasure ν
inst✝ : ν.HaveLebesgueDecomposition μ
r : ℝ≥0∞
hr : r ≠ 0
hr_ne_top : r ≠ ⊤
⊢ r.toNNReal ≠ 0

Tactic:
rw [ne_eq, ENNReal.toNNReal_eq_zero_iff]

Result:
α : Type u_1
m : MeasurableSpace α
ν μ : Measure α
inst✝¹ : IsFiniteMeasure ν
inst✝ : ν.HaveLebesgueDecomposition μ
r : ℝ≥0∞
hr : r ≠ 0
hr_ne_top : r ≠ ⊤
⊢ ¬(r = 0 ∨ r = ⊤)

Proof state:
case h
α : Type u_1
m : MeasurableSpace α
ν μ : Measure α
inst✝¹ : IsFiniteMeasure ν
inst✝ : ν.HaveLebesgueDecomposition μ
r : ℝ≥0∞
hr : r ≠ 0
hr_ne_top : r ≠ ⊤
h : ν.rnDeriv (r.toNNReal • μ) =ᶠ[ae μ] r.toNNReal⁻¹ • ν.rnDeriv μ
x : α
⊢ ↑r.toNNReal⁻¹ * ν.rnDeriv μ x = r⁻¹ * ν.rnDeriv μ x

Tactic:
rw [ENNReal.coe_inv, ENNReal.coe_toNNReal hr_ne_top]

Result:
case h
α : Type u_1
m : MeasurableSpace α
ν μ : Measure α
inst✝¹ : IsFiniteMeasure ν
inst✝ : ν.HaveLebesgueDecomposition μ
r : ℝ≥0∞
hr : r ≠ 0
hr_ne_top : r ≠ ⊤
h : ν.rnDeriv (r.toNNReal • μ) =ᶠ[ae μ] r.toNNReal⁻¹ • ν.rnDeriv μ
x : α
⊢ r.toNNReal ≠ 0

Proof state:
case h
α : Type u_1
m : MeasurableSpace α
ν μ : Measure α
inst✝¹ : IsFiniteMeasure ν
inst✝ : ν.HaveLebesgueDecomposition μ
r : ℝ≥0∞
hr : r ≠ 0
hr_ne_top : r ≠ ⊤
h : ν.rnDeriv (r.toNNReal • μ) =ᶠ[ae μ] r.toNNReal⁻¹ • ν.rnDeriv μ
x : α
⊢ ¬(r = 0 ∨ r = ⊤)

Tactic:
simp [hr, hr_ne_top]

Result:
no goals

Proof state:
α : Type u_1
m : MeasurableSpace α
ν μ : Measure α
inst✝¹ : IsFiniteMeasure ν
inst✝ : ν.HaveLebesgueDecomposition μ
r : ℝ≥0∞
hr : r ≠ 0
hr_ne_top : r ≠ ⊤
⊢ ¬(r = 0 ∨ r = ⊤)

Tactic:
simp [hr, hr_ne_top]

Result:
no goals

Proof state:
case h
α : Type u_1
m : MeasurableSpace α
ν μ : Measure α
inst✝¹ : IsFiniteMeasure ν
inst✝ : ν.HaveLebesgueDecomposition μ
r : ℝ≥0∞
hr : r ≠ 0
hr_ne_top : r ≠ ⊤
h : ν.rnDeriv (r.toNNReal • μ) =ᶠ[ae μ] r.toNNReal⁻¹ • ν.rnDeriv μ
x : α
⊢ (r.toNNReal⁻¹ • ν.rnDeriv μ) x = (r⁻¹ • ν.rnDeriv μ) x

Tactic:
simp only [Pi.smul_apply, ENNReal.smul_def, ne_eq, smul_eq_mul]

Result:
case h
α : Type u_1
m : MeasurableSpace α
ν μ : Measure α
inst✝¹ : IsFiniteMeasure ν
inst✝ : ν.HaveLebesgueDecomposition μ
r : ℝ≥0∞
hr : r ≠ 0
hr_ne_top : r ≠ ⊤
h : ν.rnDeriv (r.toNNReal • μ) =ᶠ[ae μ] r.toNNReal⁻¹ • ν.rnDeriv μ
x : α
⊢ ↑r.toNNReal⁻¹ * ν.rnDeriv μ x = r⁻¹ * ν.rnDeriv μ x

Proof state:
α : Type u_1
m : MeasurableSpace α
ν μ : Measure α
inst✝¹ : IsFiniteMeasure ν
inst✝ : ν.HaveLebesgueDecomposition μ
r : ℝ≥0∞
hr : r ≠ 0
hr_ne_top : r ≠ ⊤
⊢ ν.rnDeriv (r.toNNReal • μ) =ᶠ[ae μ] r.toNNReal⁻¹ • ν.rnDeriv μ

Tactic:
refine rnDeriv_smul_right ν μ ?_

Result:
α : Type u_1
m : MeasurableSpace α
ν μ : Measure α
inst✝¹ : IsFiniteMeasure ν
inst✝ : ν.HaveLebesgueDecomposition μ
r : ℝ≥0∞
hr : r ≠ 0
hr_ne_top : r ≠ ⊤
⊢ r.toNNReal ≠ 0

Proof state:
α : Type u_1
m : MeasurableSpace α
ν μ : Measure α
inst✝¹ : IsFiniteMeasure ν
inst✝ : ν.HaveLebesgueDecomposition μ
r : ℝ≥0∞
hr : r ≠ 0
hr_ne_top : r ≠ ⊤
h : ν.rnDeriv (r.toNNReal • μ) =ᶠ[ae μ] r.toNNReal⁻¹ • ν.rnDeriv μ
⊢ ν.rnDeriv (r • μ) =ᶠ[ae μ] r⁻¹ • ν.rnDeriv μ

Tactic:
have : (r.toNNReal)⁻¹ • rnDeriv ν μ = r⁻¹ • rnDeriv ν μ := by
  ext x
  simp only [Pi.smul_apply, ENNReal.smul_def, ne_eq, smul_eq_mul]
  rw [ENNReal.coe_inv, ENNReal.coe_toNNReal hr_ne_top]
  rw [ne_eq, ENNReal.toNNReal_eq_zero_iff]
  simp [hr, hr_ne_top]

Result:
α : Type u_1
m : MeasurableSpace α
ν μ : Measure α
inst✝¹ : IsFiniteMeasure ν
inst✝ : ν.HaveLebesgueDecomposition μ
r : ℝ≥0∞
hr : r ≠ 0
hr_ne_top : r ≠ ⊤
h : ν.rnDeriv (r.toNNReal • μ) =ᶠ[ae μ] r.toNNReal⁻¹ • ν.rnDeriv μ
this : r.toNNReal⁻¹ • ν.rnDeriv μ = r⁻¹ • ν.rnDeriv μ
⊢ ν.rnDeriv (r • μ) =ᶠ[ae μ] r⁻¹ • ν.rnDeriv μ

Proof state:
case h
α : Type u_1
m : MeasurableSpace α
ν μ : Measure α
inst✝¹ : IsFiniteMeasure ν
inst✝ : ν.HaveLebesgueDecomposition μ
r : ℝ≥0∞
hr : r ≠ 0
hr_ne_top : r ≠ ⊤
h : ν.rnDeriv (r.toNNReal • μ) =ᶠ[ae μ] r.toNNReal⁻¹ • ν.rnDeriv μ
x : α
⊢ r.toNNReal ≠ 0

Tactic:
rw [ne_eq, ENNReal.toNNReal_eq_zero_iff]

Result:
case h
α : Type u_1
m : MeasurableSpace α
ν μ : Measure α
inst✝¹ : IsFiniteMeasure ν
inst✝ : ν.HaveLebesgueDecomposition μ
r : ℝ≥0∞
hr : r ≠ 0
hr_ne_top : r ≠ ⊤
h : ν.rnDeriv (r.toNNReal • μ) =ᶠ[ae μ] r.toNNReal⁻¹ • ν.rnDeriv μ
x : α
⊢ ¬(r = 0 ∨ r = ⊤)

Proof state:
α : Type u_1
m : MeasurableSpace α
ν μ : Measure α
inst✝¹ : IsFiniteMeasure ν
inst✝ : ν.HaveLebesgueDecomposition μ
r : ℝ≥0∞
hr : r ≠ 0
hr_ne_top : r ≠ ⊤
⊢ ν.rnDeriv (r • μ) =ᶠ[ae μ] r⁻¹ • ν.rnDeriv μ

Tactic:
have h : ν.rnDeriv (r.toNNReal • μ) =ᵐ[μ] r.toNNReal⁻¹ • ν.rnDeriv μ := by
  refine rnDeriv_smul_right ν μ ?_
  rw [ne_eq, ENNReal.toNNReal_eq_zero_iff]
  simp [hr, hr_ne_top]

Result:
α : Type u_1
m : MeasurableSpace α
ν μ : Measure α
inst✝¹ : IsFiniteMeasure ν
inst✝ : ν.HaveLebesgueDecomposition μ
r : ℝ≥0∞
hr : r ≠ 0
hr_ne_top : r ≠ ⊤
h : ν.rnDeriv (r.toNNReal • μ) =ᶠ[ae μ] r.toNNReal⁻¹ • ν.rnDeriv μ
⊢ ν.rnDeriv (r • μ) =ᶠ[ae μ] r⁻¹ • ν.rnDeriv μ

Proof state:
α : Type u_1
m : MeasurableSpace α
ν μ : Measure α
inst✝¹ : IsFiniteMeasure ν
inst✝ : ν.HaveLebesgueDecomposition μ
r : ℝ≥0∞
hr : r ≠ 0
hr_ne_top : r ≠ ⊤
h : ν.rnDeriv (r.toNNReal • μ) =ᶠ[ae μ] r.toNNReal⁻¹ • ν.rnDeriv μ
⊢ r.toNNReal⁻¹ • ν.rnDeriv μ = r⁻¹ • ν.rnDeriv μ

Tactic:
ext x

Result:
case h
α : Type u_1
m : MeasurableSpace α
ν μ : Measure α
inst✝¹ : IsFiniteMeasure ν
inst✝ : ν.HaveLebesgueDecomposition μ
r : ℝ≥0∞
hr : r ≠ 0
hr_ne_top : r ≠ ⊤
h : ν.rnDeriv (r.toNNReal • μ) =ᶠ[ae μ] r.toNNReal⁻¹ • ν.rnDeriv μ
x : α
⊢ (r.toNNReal⁻¹ • ν.rnDeriv μ) x = (r⁻¹ • ν.rnDeriv μ) x

Proof state:
α : Type u_1
m : MeasurableSpace α
ν μ : Measure α
inst✝¹ : IsFiniteMeasure ν
inst✝ : ν.HaveLebesgueDecomposition μ
r : ℝ≥0∞
hr : r ≠ 0
hr_ne_top : r ≠ ⊤
h : ν.rnDeriv (r.toNNReal • μ) =ᶠ[ae μ] r.toNNReal⁻¹ • ν.rnDeriv μ
this : r.toNNReal⁻¹ • ν.rnDeriv μ = r⁻¹ • ν.rnDeriv μ
⊢ ν.rnDeriv (r • μ) =ᶠ[ae μ] r⁻¹ • ν.rnDeriv μ

Tactic:
simp_rw [this, ENNReal.smul_def, ENNReal.coe_toNNReal hr_ne_top] at h

Result:
α : Type u_1
m : MeasurableSpace α
ν μ : Measure α
inst✝¹ : IsFiniteMeasure ν
inst✝ : ν.HaveLebesgueDecomposition μ
r : ℝ≥0∞
hr : r ≠ 0
hr_ne_top : r ≠ ⊤
this : r.toNNReal⁻¹ • ν.rnDeriv μ = r⁻¹ • ν.rnDeriv μ
h : ν.rnDeriv (r • μ) =ᶠ[ae μ] r⁻¹ • ν.rnDeriv μ
⊢ ν.rnDeriv (r • μ) =ᶠ[ae μ] r⁻¹ • ν.rnDeriv μ

Proof state:
α : Type u_1
m : MeasurableSpace α
ν μ : Measure α
inst✝¹ : IsFiniteMeasure ν
inst✝ : ν.HaveLebesgueDecomposition μ
r : ℝ≥0∞
hr : r ≠ 0
hr_ne_top : r ≠ ⊤
this : r.toNNReal⁻¹ • ν.rnDeriv μ = r⁻¹ • ν.rnDeriv μ
h : ν.rnDeriv (r • μ) =ᶠ[ae μ] r⁻¹ • ν.rnDeriv μ
⊢ ν.rnDeriv (r • μ) =ᶠ[ae μ] r⁻¹ • ν.rnDeriv μ

Tactic:
exact h

Result:
no goals