-- Mathlib/MeasureTheory/VectorMeasure/WithDensity.lean
theorem withDensityᵥ_smul {𝕜 : Type*} [NontriviallyNormedField 𝕜] [NormedSpace 𝕜 E]
    [SMulCommClass ℝ 𝕜 E] (f : α → E) (r : 𝕜) : μ.withDensityᵥ (r • f) = r • μ.withDensityᵥ f

Proof state:
case pos
α : Type u_1
m : MeasurableSpace α
μ : Measure α
E : Type u_2
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
𝕜 : Type u_3
inst✝² : NontriviallyNormedField 𝕜
inst✝¹ : NormedSpace 𝕜 E
inst✝ : SMulCommClass ℝ 𝕜 E
f : α → E
r : 𝕜
hf : Integrable f μ
⊢ μ.withDensityᵥ (r • f) = r • μ.withDensityᵥ f

Tactic:
ext1 i hi

Result:
case pos.h
α : Type u_1
m : MeasurableSpace α
μ : Measure α
E : Type u_2
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
𝕜 : Type u_3
inst✝² : NontriviallyNormedField 𝕜
inst✝¹ : NormedSpace 𝕜 E
inst✝ : SMulCommClass ℝ 𝕜 E
f : α → E
r : 𝕜
hf : Integrable f μ
i : Set α
hi : MeasurableSet i
⊢ ↑(μ.withDensityᵥ (r • f)) i = ↑(r • μ.withDensityᵥ f) i

Proof state:
α : Type u_1
m : MeasurableSpace α
μ : Measure α
E : Type u_2
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
𝕜 : Type u_3
inst✝² : NontriviallyNormedField 𝕜
inst✝¹ : NormedSpace 𝕜 E
inst✝ : SMulCommClass ℝ 𝕜 E
f : α → E
r : 𝕜
⊢ μ.withDensityᵥ (r • f) = r • μ.withDensityᵥ f

Tactic:
by_cases hf : Integrable f μ

Result:
case pos
α : Type u_1
m : MeasurableSpace α
μ : Measure α
E : Type u_2
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
𝕜 : Type u_3
inst✝² : NontriviallyNormedField 𝕜
inst✝¹ : NormedSpace 𝕜 E
inst✝ : SMulCommClass ℝ 𝕜 E
f : α → E
r : 𝕜
hf : Integrable f μ
⊢ μ.withDensityᵥ (r • f) = r • μ.withDensityᵥ f

case neg
α : Type u_1
m : MeasurableSpace α
μ : Measure α
E : Type u_2
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
𝕜 : Type u_3
inst✝² : NontriviallyNormedField 𝕜
inst✝¹ : NormedSpace 𝕜 E
inst✝ : SMulCommClass ℝ 𝕜 E
f : α → E
r : 𝕜
hf : ¬Integrable f μ
⊢ μ.withDensityᵥ (r • f) = r • μ.withDensityᵥ f

Proof state:
case pos.h
α : Type u_1
m : MeasurableSpace α
μ : Measure α
E : Type u_2
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
𝕜 : Type u_3
inst✝² : NontriviallyNormedField 𝕜
inst✝¹ : NormedSpace 𝕜 E
inst✝ : SMulCommClass ℝ 𝕜 E
f : α → E
r : 𝕜
hf : Integrable f μ
i : Set α
hi : MeasurableSet i
⊢ ∫ (x : α) in i, (r • f) x ∂μ = ∫ (a : α) in i, r • f a ∂μ

Tactic:
simp only [Pi.smul_apply]

Result:
no goals

Proof state:
case neg
α : Type u_1
m : MeasurableSpace α
μ : Measure α
E : Type u_2
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
𝕜 : Type u_3
inst✝² : NontriviallyNormedField 𝕜
inst✝¹ : NormedSpace 𝕜 E
inst✝ : SMulCommClass ℝ 𝕜 E
f : α → E
r : 𝕜
hf : ¬Integrable f μ
hr : ¬r = 0
⊢ μ.withDensityᵥ (r • f) = r • μ.withDensityᵥ f

Tactic:
rw [withDensityᵥ, withDensityᵥ, dif_neg hf, dif_neg, smul_zero]

Result:
case neg.hnc
α : Type u_1
m : MeasurableSpace α
μ : Measure α
E : Type u_2
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
𝕜 : Type u_3
inst✝² : NontriviallyNormedField 𝕜
inst✝¹ : NormedSpace 𝕜 E
inst✝ : SMulCommClass ℝ 𝕜 E
f : α → E
r : 𝕜
hf : ¬Integrable f μ
hr : ¬r = 0
⊢ ¬Integrable (r • f) μ

Proof state:
case pos.h
α : Type u_1
m : MeasurableSpace α
μ : Measure α
E : Type u_2
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
𝕜 : Type u_3
inst✝² : NontriviallyNormedField 𝕜
inst✝¹ : NormedSpace 𝕜 E
inst✝ : SMulCommClass ℝ 𝕜 E
f : α → E
r : 𝕜
hf : Integrable f μ
i : Set α
hi : MeasurableSet i
⊢ ↑(μ.withDensityᵥ (r • f)) i = ↑(r • μ.withDensityᵥ f) i

Tactic:
rw [withDensityᵥ_apply (hf.smul r) hi, VectorMeasure.smul_apply, withDensityᵥ_apply hf hi, ←
  integral_smul r f]

Result:
case pos.h
α : Type u_1
m : MeasurableSpace α
μ : Measure α
E : Type u_2
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
𝕜 : Type u_3
inst✝² : NontriviallyNormedField 𝕜
inst✝¹ : NormedSpace 𝕜 E
inst✝ : SMulCommClass ℝ 𝕜 E
f : α → E
r : 𝕜
hf : Integrable f μ
i : Set α
hi : MeasurableSet i
⊢ ∫ (x : α) in i, (r • f) x ∂μ = ∫ (a : α) in i, r • f a ∂μ

Proof state:
case neg
α : Type u_1
m : MeasurableSpace α
μ : Measure α
E : Type u_2
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
𝕜 : Type u_3
inst✝² : NontriviallyNormedField 𝕜
inst✝¹ : NormedSpace 𝕜 E
inst✝ : SMulCommClass ℝ 𝕜 E
f : α → E
r : 𝕜
hf : ¬Integrable f μ
⊢ μ.withDensityᵥ (r • f) = r • μ.withDensityᵥ f

Tactic:
by_cases hr : r = 0

Result:
case pos
α : Type u_1
m : MeasurableSpace α
μ : Measure α
E : Type u_2
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
𝕜 : Type u_3
inst✝² : NontriviallyNormedField 𝕜
inst✝¹ : NormedSpace 𝕜 E
inst✝ : SMulCommClass ℝ 𝕜 E
f : α → E
r : 𝕜
hf : ¬Integrable f μ
hr : r = 0
⊢ μ.withDensityᵥ (r • f) = r • μ.withDensityᵥ f

case neg
α : Type u_1
m : MeasurableSpace α
μ : Measure α
E : Type u_2
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
𝕜 : Type u_3
inst✝² : NontriviallyNormedField 𝕜
inst✝¹ : NormedSpace 𝕜 E
inst✝ : SMulCommClass ℝ 𝕜 E
f : α → E
r : 𝕜
hf : ¬Integrable f μ
hr : ¬r = 0
⊢ μ.withDensityᵥ (r • f) = r • μ.withDensityᵥ f

Proof state:
case neg.hnc
α : Type u_1
m : MeasurableSpace α
μ : Measure α
E : Type u_2
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
𝕜 : Type u_3
inst✝² : NontriviallyNormedField 𝕜
inst✝¹ : NormedSpace 𝕜 E
inst✝ : SMulCommClass ℝ 𝕜 E
f : α → E
r : 𝕜
hf : ¬Integrable f μ
hr : ¬r = 0
⊢ ¬Integrable (r • f) μ

Tactic:
rwa [integrable_smul_iff hr f]

Result:
no goals

Proof state:
case pos
α : Type u_1
m : MeasurableSpace α
μ : Measure α
E : Type u_2
inst✝⁴ : NormedAddCommGroup E
inst✝³ : NormedSpace ℝ E
𝕜 : Type u_3
inst✝² : NontriviallyNormedField 𝕜
inst✝¹ : NormedSpace 𝕜 E
inst✝ : SMulCommClass ℝ 𝕜 E
f : α → E
r : 𝕜
hf : ¬Integrable f μ
hr : r = 0
⊢ μ.withDensityᵥ (r • f) = r • μ.withDensityᵥ f

Tactic:
rw [hr, zero_smul, zero_smul, withDensityᵥ_zero]

Result:
no goals