Theorem: MeasureTheory.integral_comp_mul_left_Ioi
File: Mathlib/MeasureTheory/Integral/IntegralEqImproper.lean

Proof steps:
state_before: E : Type u_1
f : ℝ → E
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
g : ℝ → E
a b : ℝ
hb : 0 < b
⊢ ∫ (x : ℝ) in Ioi a, g (b * x) = b⁻¹ • ∫ (x : ℝ) in Ioi (b * a), g x
state_after: E : Type u_1
f : ℝ → E
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
g : ℝ → E
a b : ℝ
hb : 0 < b
this : ∀ (c : ℝ), MeasurableSet (Ioi c)
⊢ ∫ (x : ℝ) in Ioi a, g (b * x) = b⁻¹ • ∫ (x : ℝ) in Ioi (b * a), g x
tactic: have : ∀ c : ℝ, MeasurableSet (Ioi c) := fun c => measurableSet_Ioi
state_before: E : Type u_1
f : ℝ → E
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
g : ℝ → E
a b : ℝ
hb : 0 < b
this : ∀ (c : ℝ), MeasurableSet (Ioi c)
⊢ ∫ (x : ℝ) in Ioi a, g (b * x) = b⁻¹ • ∫ (x : ℝ) in Ioi (b * a), g x
state_after: E : Type u_1
f : ℝ → E
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
g : ℝ → E
a b : ℝ
hb : 0 < b
this : ∀ (c : ℝ), MeasurableSet (Ioi c)
⊢ ∫ (x : ℝ), (Ioi a).indicator (fun x => g (b * x)) x ∂volume = ∫ (x : ℝ), (Ioi (b * a)).indicator g (b * x)
tactic: rw [← integral_indicator (this a), ← integral_indicator (this (b * a)),
    ← abs_of_pos (inv_pos.mpr hb), ← Measure.integral_comp_mul_left]
state_before: E : Type u_1
f : ℝ → E
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
g : ℝ → E
a b : ℝ
hb : 0 < b
this : ∀ (c : ℝ), MeasurableSet (Ioi c)
⊢ ∫ (x : ℝ), (Ioi a).indicator (fun x => g (b * x)) x ∂volume = ∫ (x : ℝ), (Ioi (b * a)).indicator g (b * x)
state_after: case e_f
E : Type u_1
f : ℝ → E
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
g : ℝ → E
a b : ℝ
hb : 0 < b
this : ∀ (c : ℝ), MeasurableSet (Ioi c)
⊢ (fun x => (Ioi a).indicator (fun x => g (b * x)) x) = fun x => (Ioi (b * a)).indicator g (b * x)
tactic: congr
state_before: case e_f
E : Type u_1
f : ℝ → E
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
g : ℝ → E
a b : ℝ
hb : 0 < b
this : ∀ (c : ℝ), MeasurableSet (Ioi c)
⊢ (fun x => (Ioi a).indicator (fun x => g (b * x)) x) = fun x => (Ioi (b * a)).indicator g (b * x)
state_after: case e_f.h
E : Type u_1
f : ℝ → E
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
g : ℝ → E
a b : ℝ
hb : 0 < b
this : ∀ (c : ℝ), MeasurableSet (Ioi c)
x : ℝ
⊢ (Ioi a).indicator (fun x => g (b * x)) x = (Ioi (b * a)).indicator g (b * x)
tactic: ext1 x
state_before: case e_f.h
E : Type u_1
f : ℝ → E
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
g : ℝ → E
a b : ℝ
hb : 0 < b
this : ∀ (c : ℝ), MeasurableSet (Ioi c)
x : ℝ
⊢ (Ioi a).indicator (fun x => g (b * x)) x = (Ioi (b * a)).indicator g (b * x)
state_after: case e_f.h
E : Type u_1
f : ℝ → E
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
g : ℝ → E
a b : ℝ
hb : 0 < b
this : ∀ (c : ℝ), MeasurableSet (Ioi c)
x : ℝ
⊢ (Ioi a).indicator (fun x => g (b * x)) x = (Ioi a).indicator (g ∘ HMul.hMul b) x
tactic: rw [← indicator_comp_right, preimage_const_mul_Ioi _ hb, mul_div_cancel_left₀ _ hb.ne']
state_before: case e_f.h
E : Type u_1
f : ℝ → E
inst✝¹ : NormedAddCommGroup E
inst✝ : NormedSpace ℝ E
g : ℝ → E
a b : ℝ
hb : 0 < b
this : ∀ (c : ℝ), MeasurableSet (Ioi c)
x : ℝ
⊢ (Ioi a).indicator (fun x => g (b * x)) x = (Ioi a).indicator (g ∘ HMul.hMul b) x
state_after: no goals
tactic: rfl