-- Mathlib/MeasureTheory/Measure/Lebesgue/EqHaar.lean
theorem map_linearMap_addHaar_eq_smul_addHaar {f : E →ₗ[ℝ] E} (hf : LinearMap.det f ≠ 0) :
    Measure.map f μ = ENNReal.ofReal |(LinearMap.det f)⁻¹| • μ

Proof state:
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
f : E →ₗ[ℝ] E
hf : LinearMap.det f ≠ 0
ι : Type := Fin (finrank ℝ E)
this✝ : FiniteDimensional ℝ (ι → ℝ)
this : finrank ℝ E = finrank ℝ (ι → ℝ)
e : E ≃ₗ[ℝ] ι → ℝ
g : (ι → ℝ) →ₗ[ℝ] ι → ℝ
hg : g = ↑e ∘ₗ f ∘ₗ ↑e.symm
⊢ LinearMap.det g = LinearMap.det f

Tactic:
rw [hg]

Result:
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
f : E →ₗ[ℝ] E
hf : LinearMap.det f ≠ 0
ι : Type := Fin (finrank ℝ E)
this✝ : FiniteDimensional ℝ (ι → ℝ)
this : finrank ℝ E = finrank ℝ (ι → ℝ)
e : E ≃ₗ[ℝ] ι → ℝ
g : (ι → ℝ) →ₗ[ℝ] ι → ℝ
hg : g = ↑e ∘ₗ f ∘ₗ ↑e.symm
⊢ LinearMap.det (↑e ∘ₗ f ∘ₗ ↑e.symm) = LinearMap.det f

Proof state:
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
f : E →ₗ[ℝ] E
ι : Type := Fin (finrank ℝ E)
this✝ : FiniteDimensional ℝ (ι → ℝ)
this : finrank ℝ E = finrank ℝ (ι → ℝ)
e : E ≃ₗ[ℝ] ι → ℝ
g : (ι → ℝ) →ₗ[ℝ] ι → ℝ
hf : LinearMap.det g ≠ 0
hg : g = ↑e ∘ₗ f ∘ₗ ↑e.symm
gdet : LinearMap.det g = LinearMap.det f
⊢ f = ↑e.symm ∘ₗ g ∘ₗ ↑e

Tactic:
ext x

Result:
case h
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
f : E →ₗ[ℝ] E
ι : Type := Fin (finrank ℝ E)
this✝ : FiniteDimensional ℝ (ι → ℝ)
this : finrank ℝ E = finrank ℝ (ι → ℝ)
e : E ≃ₗ[ℝ] ι → ℝ
g : (ι → ℝ) →ₗ[ℝ] ι → ℝ
hf : LinearMap.det g ≠ 0
hg : g = ↑e ∘ₗ f ∘ₗ ↑e.symm
gdet : LinearMap.det g = LinearMap.det f
x : E
⊢ f x = (↑e.symm ∘ₗ g ∘ₗ ↑e) x

Proof state:
case intro
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
f : E →ₗ[ℝ] E
hf : LinearMap.det f ≠ 0
ι : Type := Fin (finrank ℝ E)
this✝ : FiniteDimensional ℝ (ι → ℝ)
this : finrank ℝ E = finrank ℝ (ι → ℝ)
e : E ≃ₗ[ℝ] ι → ℝ
g : (ι → ℝ) →ₗ[ℝ] ι → ℝ
hg : g = ↑e ∘ₗ f ∘ₗ ↑e.symm
gdet : LinearMap.det g = LinearMap.det f
⊢ map (⇑f) μ = ENNReal.ofReal |(LinearMap.det f)⁻¹| • μ

Tactic:
rw [← gdet] at hf ⊢

Result:
case intro
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
f : E →ₗ[ℝ] E
ι : Type := Fin (finrank ℝ E)
this✝ : FiniteDimensional ℝ (ι → ℝ)
this : finrank ℝ E = finrank ℝ (ι → ℝ)
e : E ≃ₗ[ℝ] ι → ℝ
g : (ι → ℝ) →ₗ[ℝ] ι → ℝ
hf : LinearMap.det g ≠ 0
hg : g = ↑e ∘ₗ f ∘ₗ ↑e.symm
gdet : LinearMap.det g = LinearMap.det f
⊢ map (⇑f) μ = ENNReal.ofReal |(LinearMap.det g)⁻¹| • μ

Proof state:
case h
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
f : E →ₗ[ℝ] E
ι : Type := Fin (finrank ℝ E)
this✝ : FiniteDimensional ℝ (ι → ℝ)
this : finrank ℝ E = finrank ℝ (ι → ℝ)
e : E ≃ₗ[ℝ] ι → ℝ
g : (ι → ℝ) →ₗ[ℝ] ι → ℝ
hf : LinearMap.det g ≠ 0
hg : g = ↑e ∘ₗ f ∘ₗ ↑e.symm
gdet : LinearMap.det g = LinearMap.det f
x : E
⊢ f x = (↑e.symm ∘ₗ g ∘ₗ ↑e) x

Tactic:
simp only [LinearEquiv.coe_coe, Function.comp_apply, LinearMap.coe_comp,
  LinearEquiv.symm_apply_apply, hg]

Result:
no goals

Proof state:
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
f : E →ₗ[ℝ] E
hf : LinearMap.det f ≠ 0
ι : Type := Fin (finrank ℝ E)
this : FiniteDimensional ℝ (ι → ℝ)
⊢ map (⇑f) μ = ENNReal.ofReal |(LinearMap.det f)⁻¹| • μ

Tactic:
have : finrank ℝ E = finrank ℝ (ι → ℝ) := by simp [ι]

Result:
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
f : E →ₗ[ℝ] E
hf : LinearMap.det f ≠ 0
ι : Type := Fin (finrank ℝ E)
this✝ : FiniteDimensional ℝ (ι → ℝ)
this : finrank ℝ E = finrank ℝ (ι → ℝ)
⊢ map (⇑f) μ = ENNReal.ofReal |(LinearMap.det f)⁻¹| • μ

Proof state:
case intro
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
f : E →ₗ[ℝ] E
ι : Type := Fin (finrank ℝ E)
this✝ : FiniteDimensional ℝ (ι → ℝ)
this : finrank ℝ E = finrank ℝ (ι → ℝ)
e : E ≃ₗ[ℝ] ι → ℝ
g : (ι → ℝ) →ₗ[ℝ] ι → ℝ
hf : LinearMap.det g ≠ 0
hg : g = ↑e ∘ₗ f ∘ₗ ↑e.symm
gdet : LinearMap.det g = LinearMap.det f
fg : f = ↑e.symm ∘ₗ g ∘ₗ ↑e
Ce : Continuous ⇑e
Cg : Continuous ⇑g
Cesymm : Continuous ⇑e.symm
⊢ map (⇑e.symm ∘ ⇑g ∘ ⇑e) μ = ENNReal.ofReal |(LinearMap.det g)⁻¹| • μ

Tactic:
rw [← map_map Cesymm.measurable (Cg.comp Ce).measurable, ← map_map Cg.measurable Ce.measurable]

Result:
case intro
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
f : E →ₗ[ℝ] E
ι : Type := Fin (finrank ℝ E)
this✝ : FiniteDimensional ℝ (ι → ℝ)
this : finrank ℝ E = finrank ℝ (ι → ℝ)
e : E ≃ₗ[ℝ] ι → ℝ
g : (ι → ℝ) →ₗ[ℝ] ι → ℝ
hf : LinearMap.det g ≠ 0
hg : g = ↑e ∘ₗ f ∘ₗ ↑e.symm
gdet : LinearMap.det g = LinearMap.det f
fg : f = ↑e.symm ∘ₗ g ∘ₗ ↑e
Ce : Continuous ⇑e
Cg : Continuous ⇑g
Cesymm : Continuous ⇑e.symm
⊢ map (⇑e.symm) (map (⇑g) (map (⇑e) μ)) = ENNReal.ofReal |(LinearMap.det g)⁻¹| • μ

Proof state:
case intro
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
f : E →ₗ[ℝ] E
ι : Type := Fin (finrank ℝ E)
this✝ : FiniteDimensional ℝ (ι → ℝ)
this : finrank ℝ E = finrank ℝ (ι → ℝ)
e : E ≃ₗ[ℝ] ι → ℝ
g : (ι → ℝ) →ₗ[ℝ] ι → ℝ
hf : LinearMap.det g ≠ 0
hg : g = ↑e ∘ₗ f ∘ₗ ↑e.symm
gdet : LinearMap.det g = LinearMap.det f
⊢ map (⇑f) μ = ENNReal.ofReal |(LinearMap.det g)⁻¹| • μ

Tactic:
have fg : f = (e.symm : (ι → ℝ) →ₗ[ℝ] E).comp (g.comp (e : E →ₗ[ℝ] ι → ℝ)) := by
  ext x
  simp only [LinearEquiv.coe_coe, Function.comp_apply, LinearMap.coe_comp,
    LinearEquiv.symm_apply_apply, hg]

Result:
case intro
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
f : E →ₗ[ℝ] E
ι : Type := Fin (finrank ℝ E)
this✝ : FiniteDimensional ℝ (ι → ℝ)
this : finrank ℝ E = finrank ℝ (ι → ℝ)
e : E ≃ₗ[ℝ] ι → ℝ
g : (ι → ℝ) →ₗ[ℝ] ι → ℝ
hf : LinearMap.det g ≠ 0
hg : g = ↑e ∘ₗ f ∘ₗ ↑e.symm
gdet : LinearMap.det g = LinearMap.det f
fg : f = ↑e.symm ∘ₗ g ∘ₗ ↑e
⊢ map (⇑f) μ = ENNReal.ofReal |(LinearMap.det g)⁻¹| • μ

Proof state:
E : Type u_1
inst✝⁵ : NormedAddCommGroup E
inst✝⁴ : NormedSpace ℝ E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : FiniteDimensional ℝ E
μ : Measure E
inst✝ : μ.IsAddHaarMeasure
f : E →ₗ[ℝ] E
hf : LinearMap.det f ≠ 0
ι : Type := Fin (finrank ℝ E)
this : FiniteDimensional ℝ (ι → ℝ)
⊢ finrank ℝ E = finrank ℝ (ι → ℝ)

Tactic:
simp [ι]

Result:
no goals