-- Mathlib/MeasureTheory/Group/Prod.lean
theorem measure_mul_lintegral_eq [IsMulLeftInvariant ν] (sm : MeasurableSet s) (f : G → ℝ≥0∞)
    (hf : Measurable f) : (μ s * ∫⁻ y, f y ∂ν) = ∫⁻ x, ν ((fun z => z * x) ⁻¹' s) * f x⁻¹ ∂μ

Proof state:
G : Type u_1
inst✝⁷ : MeasurableSpace G
inst✝⁶ : Group G
inst✝⁵ : MeasurableMul₂ G
μ ν : Measure G
inst✝⁴ : SFinite ν
inst✝³ : SFinite μ
s : Set G
inst✝² : MeasurableInv G
inst✝¹ : μ.IsMulLeftInvariant
inst✝ : ν.IsMulLeftInvariant
sm : MeasurableSet s
f : G → ℝ≥0∞
hf : Measurable f
ms : ∀ (x : G), Measurable fun y => ((fun z => z * x) ⁻¹' s).indicator (fun x => 1) y
x y : G
⊢ s.indicator (fun x => 1) (y * x) = ((fun z => z * x) ⁻¹' s).indicator (fun b => 1) y

Tactic:
symm

Result:
G : Type u_1
inst✝⁷ : MeasurableSpace G
inst✝⁶ : Group G
inst✝⁵ : MeasurableMul₂ G
μ ν : Measure G
inst✝⁴ : SFinite ν
inst✝³ : SFinite μ
s : Set G
inst✝² : MeasurableInv G
inst✝¹ : μ.IsMulLeftInvariant
inst✝ : ν.IsMulLeftInvariant
sm : MeasurableSet s
f : G → ℝ≥0∞
hf : Measurable f
ms : ∀ (x : G), Measurable fun y => ((fun z => z * x) ⁻¹' s).indicator (fun x => 1) y
x y : G
⊢ ((fun z => z * x) ⁻¹' s).indicator (fun b => 1) y = s.indicator (fun x => 1) (y * x)

Proof state:
G : Type u_1
inst✝⁷ : MeasurableSpace G
inst✝⁶ : Group G
inst✝⁵ : MeasurableMul₂ G
μ ν : Measure G
inst✝⁴ : SFinite ν
inst✝³ : SFinite μ
s : Set G
inst✝² : MeasurableInv G
inst✝¹ : μ.IsMulLeftInvariant
inst✝ : ν.IsMulLeftInvariant
sm : MeasurableSet s
f : G → ℝ≥0∞
hf : Measurable f
⊢ ∫⁻ (x : G), ∫⁻ (y : G), s.indicator (fun x => 1) (y * x) * f x⁻¹ ∂ν ∂μ =
    ∫⁻ (x : G), ν ((fun z => z * x) ⁻¹' s) * f x⁻¹ ∂μ

case hf
G : Type u_1
inst✝⁷ : MeasurableSpace G
inst✝⁶ : Group G
inst✝⁵ : MeasurableMul₂ G
μ ν : Measure G
inst✝⁴ : SFinite ν
inst✝³ : SFinite μ
s : Set G
inst✝² : MeasurableInv G
inst✝¹ : μ.IsMulLeftInvariant
inst✝ : ν.IsMulLeftInvariant
sm : MeasurableSet s
f : G → ℝ≥0∞
hf : Measurable f
⊢ AEMeasurable (uncurry fun x y => s.indicator (fun x => 1) x * f y) (μ.prod ν)

Tactic:
swap

Result:
case hf
G : Type u_1
inst✝⁷ : MeasurableSpace G
inst✝⁶ : Group G
inst✝⁵ : MeasurableMul₂ G
μ ν : Measure G
inst✝⁴ : SFinite ν
inst✝³ : SFinite μ
s : Set G
inst✝² : MeasurableInv G
inst✝¹ : μ.IsMulLeftInvariant
inst✝ : ν.IsMulLeftInvariant
sm : MeasurableSet s
f : G → ℝ≥0∞
hf : Measurable f
⊢ AEMeasurable (uncurry fun x y => s.indicator (fun x => 1) x * f y) (μ.prod ν)

G : Type u_1
inst✝⁷ : MeasurableSpace G
inst✝⁶ : Group G
inst✝⁵ : MeasurableMul₂ G
μ ν : Measure G
inst✝⁴ : SFinite ν
inst✝³ : SFinite μ
s : Set G
inst✝² : MeasurableInv G
inst✝¹ : μ.IsMulLeftInvariant
inst✝ : ν.IsMulLeftInvariant
sm : MeasurableSet s
f : G → ℝ≥0∞
hf : Measurable f
⊢ ∫⁻ (x : G), ∫⁻ (y : G), s.indicator (fun x => 1) (y * x) * f x⁻¹ ∂ν ∂μ =
    ∫⁻ (x : G), ν ((fun z => z * x) ⁻¹' s) * f x⁻¹ ∂μ

Proof state:
case h.e'_2.h.e'_5.h
G : Type u_1
inst✝⁷ : MeasurableSpace G
inst✝⁶ : Group G
inst✝⁵ : MeasurableMul₂ G
μ ν : Measure G
inst✝⁴ : SFinite ν
inst✝³ : SFinite μ
s : Set G
inst✝² : MeasurableInv G
inst✝¹ : μ.IsMulLeftInvariant
inst✝ : ν.IsMulLeftInvariant
sm : MeasurableSet s
f : G → ℝ≥0∞
hf : Measurable f
ms : ∀ (x : G), Measurable fun y => ((fun z => z * x) ⁻¹' s).indicator (fun x => 1) y
x y x✝ : G
⊢ 1 = ((fun x => 1) ∘ fun y => y * x) x✝

Tactic:
rfl

Result:
no goals

Proof state:
G : Type u_1
inst✝⁷ : MeasurableSpace G
inst✝⁶ : Group G
inst✝⁵ : MeasurableMul₂ G
μ ν : Measure G
inst✝⁴ : SFinite ν
inst✝³ : SFinite μ
s : Set G
inst✝² : MeasurableInv G
inst✝¹ : μ.IsMulLeftInvariant
inst✝ : ν.IsMulLeftInvariant
sm : MeasurableSet s
f : G → ℝ≥0∞
hf : Measurable f
ms : ∀ (x : G), Measurable fun y => ((fun z => z * x) ⁻¹' s).indicator (fun x => 1) y
x y : G
⊢ ((fun z => z * x) ⁻¹' s).indicator (fun b => 1) y = s.indicator (fun x => 1) (y * x)

Tactic:
convert indicator_comp_right (M := ℝ≥0∞) fun y => y * x using 2

Result:
case h.e'_2.h.e'_5
G : Type u_1
inst✝⁷ : MeasurableSpace G
inst✝⁶ : Group G
inst✝⁵ : MeasurableMul₂ G
μ ν : Measure G
inst✝⁴ : SFinite ν
inst✝³ : SFinite μ
s : Set G
inst✝² : MeasurableInv G
inst✝¹ : μ.IsMulLeftInvariant
inst✝ : ν.IsMulLeftInvariant
sm : MeasurableSet s
f : G → ℝ≥0∞
hf : Measurable f
ms : ∀ (x : G), Measurable fun y => ((fun z => z * x) ⁻¹' s).indicator (fun x => 1) y
x y : G
⊢ (fun b => 1) = (fun x => 1) ∘ fun y => y * x