Theorem: MeasureTheory.Measure.haarScalarFactor_smul
File: Mathlib/MeasureTheory/Measure/Haar/Unique.lean

Proof steps:
state_before: G : Type u_1
inst✝⁸ : TopologicalSpace G
inst✝⁷ : Group G
inst✝⁶ : TopologicalGroup G
inst✝⁵ : MeasurableSpace G
inst✝⁴ : BorelSpace G
inst✝³ : LocallyCompactSpace G
μ' μ : Measure G
inst✝² : μ.IsHaarMeasure
inst✝¹ : IsFiniteMeasureOnCompacts μ'
inst✝ : μ'.IsMulLeftInvariant
c : ℝ≥0
⊢ (c • μ').haarScalarFactor μ = c • μ'.haarScalarFactor μ
state_after: case intro.mk.intro.intro
G : Type u_1
inst✝⁸ : TopologicalSpace G
inst✝⁷ : Group G
inst✝⁶ : TopologicalGroup G
inst✝⁵ : MeasurableSpace G
inst✝⁴ : BorelSpace G
inst✝³ : LocallyCompactSpace G
μ' μ : Measure G
inst✝² : μ.IsHaarMeasure
inst✝¹ : IsFiniteMeasureOnCompacts μ'
inst✝ : μ'.IsMulLeftInvariant
c : ℝ≥0
g : G → ℝ
g_cont : Continuous g
g_comp : HasCompactSupport ⇑{ toFun := g, continuous_toFun := g_cont }
g_nonneg : 0 ≤ { toFun := g, continuous_toFun := g_cont }
g_one : { toFun := g, continuous_toFun := g_cont } 1 ≠ 0
⊢ (c • μ').haarScalarFactor μ = c • μ'.haarScalarFactor μ
tactic: obtain ⟨⟨g, g_cont⟩, g_comp, g_nonneg, g_one⟩ :
    ∃ g : C(G, ℝ), HasCompactSupport g ∧ 0 ≤ g ∧ g 1 ≠ 0 := exists_continuous_nonneg_pos 1
state_before: case intro.mk.intro.intro
G : Type u_1
inst✝⁸ : TopologicalSpace G
inst✝⁷ : Group G
inst✝⁶ : TopologicalGroup G
inst✝⁵ : MeasurableSpace G
inst✝⁴ : BorelSpace G
inst✝³ : LocallyCompactSpace G
μ' μ : Measure G
inst✝² : μ.IsHaarMeasure
inst✝¹ : IsFiniteMeasureOnCompacts μ'
inst✝ : μ'.IsMulLeftInvariant
c : ℝ≥0
g : G → ℝ
g_cont : Continuous g
g_comp : HasCompactSupport ⇑{ toFun := g, continuous_toFun := g_cont }
g_nonneg : 0 ≤ { toFun := g, continuous_toFun := g_cont }
g_one : { toFun := g, continuous_toFun := g_cont } 1 ≠ 0
⊢ (c • μ').haarScalarFactor μ = c • μ'.haarScalarFactor μ
state_after: case intro.mk.intro.intro
G : Type u_1
inst✝⁸ : TopologicalSpace G
inst✝⁷ : Group G
inst✝⁶ : TopologicalGroup G
inst✝⁵ : MeasurableSpace G
inst✝⁴ : BorelSpace G
inst✝³ : LocallyCompactSpace G
μ' μ : Measure G
inst✝² : μ.IsHaarMeasure
inst✝¹ : IsFiniteMeasureOnCompacts μ'
inst✝ : μ'.IsMulLeftInvariant
c : ℝ≥0
g : G → ℝ
g_cont : Continuous g
g_comp : HasCompactSupport ⇑{ toFun := g, continuous_toFun := g_cont }
g_nonneg : 0 ≤ { toFun := g, continuous_toFun := g_cont }
g_one : { toFun := g, continuous_toFun := g_cont } 1 ≠ 0
int_g_ne_zero : ∫ (x : G), g x ∂μ ≠ 0
⊢ (c • μ').haarScalarFactor μ = c • μ'.haarScalarFactor μ
tactic: have int_g_ne_zero : ∫ x, g x ∂μ ≠ 0 :=
    ne_of_gt (g_cont.integral_pos_of_hasCompactSupport_nonneg_nonzero g_comp g_nonneg g_one)
state_before: case intro.mk.intro.intro
G : Type u_1
inst✝⁸ : TopologicalSpace G
inst✝⁷ : Group G
inst✝⁶ : TopologicalGroup G
inst✝⁵ : MeasurableSpace G
inst✝⁴ : BorelSpace G
inst✝³ : LocallyCompactSpace G
μ' μ : Measure G
inst✝² : μ.IsHaarMeasure
inst✝¹ : IsFiniteMeasureOnCompacts μ'
inst✝ : μ'.IsMulLeftInvariant
c : ℝ≥0
g : G → ℝ
g_cont : Continuous g
g_comp : HasCompactSupport ⇑{ toFun := g, continuous_toFun := g_cont }
g_nonneg : 0 ≤ { toFun := g, continuous_toFun := g_cont }
g_one : { toFun := g, continuous_toFun := g_cont } 1 ≠ 0
int_g_ne_zero : ∫ (x : G), g x ∂μ ≠ 0
⊢ (c • μ').haarScalarFactor μ = c • μ'.haarScalarFactor μ
state_after: case intro.mk.intro.intro.a
G : Type u_1
inst✝⁸ : TopologicalSpace G
inst✝⁷ : Group G
inst✝⁶ : TopologicalGroup G
inst✝⁵ : MeasurableSpace G
inst✝⁴ : BorelSpace G
inst✝³ : LocallyCompactSpace G
μ' μ : Measure G
inst✝² : μ.IsHaarMeasure
inst✝¹ : IsFiniteMeasureOnCompacts μ'
inst✝ : μ'.IsMulLeftInvariant
c : ℝ≥0
g : G → ℝ
g_cont : Continuous g
g_comp : HasCompactSupport ⇑{ toFun := g, continuous_toFun := g_cont }
g_nonneg : 0 ≤ { toFun := g, continuous_toFun := g_cont }
g_one : { toFun := g, continuous_toFun := g_cont } 1 ≠ 0
int_g_ne_zero : ∫ (x : G), g x ∂μ ≠ 0
⊢ ↑((c • μ').haarScalarFactor μ) = ↑(c • μ'.haarScalarFactor μ)
tactic: apply NNReal.coe_injective
state_before: case intro.mk.intro.intro.a
G : Type u_1
inst✝⁸ : TopologicalSpace G
inst✝⁷ : Group G
inst✝⁶ : TopologicalGroup G
inst✝⁵ : MeasurableSpace G
inst✝⁴ : BorelSpace G
inst✝³ : LocallyCompactSpace G
μ' μ : Measure G
inst✝² : μ.IsHaarMeasure
inst✝¹ : IsFiniteMeasureOnCompacts μ'
inst✝ : μ'.IsMulLeftInvariant
c : ℝ≥0
g : G → ℝ
g_cont : Continuous g
g_comp : HasCompactSupport ⇑{ toFun := g, continuous_toFun := g_cont }
g_nonneg : 0 ≤ { toFun := g, continuous_toFun := g_cont }
g_one : { toFun := g, continuous_toFun := g_cont } 1 ≠ 0
int_g_ne_zero : ∫ (x : G), g x ∂μ ≠ 0
⊢ ↑((c • μ').haarScalarFactor μ) = ↑(c • μ'.haarScalarFactor μ)
state_after: no goals
tactic: calc
    haarScalarFactor (c • μ') μ = (∫ x, g x ∂(c • μ')) / ∫ x, g x ∂μ :=
      haarScalarFactor_eq_integral_div _ _ g_cont g_comp int_g_ne_zero
    _ = (c • (∫ x, g x ∂μ')) / ∫ x, g x ∂μ := by simp
    _ = c • ((∫ x, g x ∂μ') / ∫ x, g x ∂μ) := smul_div_assoc c _ _
    _ = c • haarScalarFactor μ' μ := by
      rw [← haarScalarFactor_eq_integral_div _ _ g_cont g_comp int_g_ne_zero]