-- Mathlib/Analysis/Convolution.lean
theorem ConvolutionExistsAt.of_norm' {x₀ : G}
    (h : ConvolutionExistsAt (fun x => ‖f x‖) (fun x => ‖g x‖) x₀ (mul ℝ ℝ) μ)
    (hmf : AEStronglyMeasurable f μ) (hmg : AEStronglyMeasurable g <| map (fun t => x₀ - t) μ) :
    ConvolutionExistsAt f g x₀ L μ

Proof state:
𝕜 : Type u𝕜
G : Type uG
E : Type uE
E' : Type uE'
F : Type uF
inst✝¹⁰ : NormedAddCommGroup E
inst✝⁹ : NormedAddCommGroup E'
inst✝⁸ : NormedAddCommGroup F
f : G → E
g : G → E'
inst✝⁷ : NontriviallyNormedField 𝕜
inst✝⁶ : NormedSpace 𝕜 E
inst✝⁵ : NormedSpace 𝕜 E'
inst✝⁴ : NormedSpace 𝕜 F
L : E →L[𝕜] E' →L[𝕜] F
inst✝³ : MeasurableSpace G
μ : Measure G
inst✝² : AddGroup G
inst✝¹ : MeasurableAdd G
inst✝ : MeasurableNeg G
x₀ : G
h : ConvolutionExistsAt (fun x => ‖f x‖) (fun x => ‖g x‖) x₀ (mul ℝ ℝ) μ
hmf : AEStronglyMeasurable f μ
hmg : AEStronglyMeasurable g (Measure.map (fun t => x₀ - t) μ)
x : G
⊢ ‖(L (f x)) (g (x₀ - x))‖ ≤ ‖L‖ * (fun x => ‖f x‖) x * (fun x => ‖g x‖) (x₀ - x)

Tactic:
apply L.le_opNorm₂

Result:
no goals

Proof state:
𝕜 : Type u𝕜
G : Type uG
E : Type uE
E' : Type uE'
F : Type uF
inst✝¹⁰ : NormedAddCommGroup E
inst✝⁹ : NormedAddCommGroup E'
inst✝⁸ : NormedAddCommGroup F
f : G → E
g : G → E'
inst✝⁷ : NontriviallyNormedField 𝕜
inst✝⁶ : NormedSpace 𝕜 E
inst✝⁵ : NormedSpace 𝕜 E'
inst✝⁴ : NormedSpace 𝕜 F
L : E →L[𝕜] E' →L[𝕜] F
inst✝³ : MeasurableSpace G
μ : Measure G
inst✝² : AddGroup G
inst✝¹ : MeasurableAdd G
inst✝ : MeasurableNeg G
x₀ : G
h : ConvolutionExistsAt (fun x => ‖f x‖) (fun x => ‖g x‖) x₀ (mul ℝ ℝ) μ
hmf : AEStronglyMeasurable f μ
hmg : AEStronglyMeasurable g (Measure.map (fun t => x₀ - t) μ)
x : G
⊢ ‖(L (f x)) (g (x₀ - x))‖ ≤ ‖L‖ * ((mul ℝ ℝ) ((fun x => ‖f x‖) x)) ((fun x => ‖g x‖) (x₀ - x))

Tactic:
rw [mul_apply', ← mul_assoc]

Result:
𝕜 : Type u𝕜
G : Type uG
E : Type uE
E' : Type uE'
F : Type uF
inst✝¹⁰ : NormedAddCommGroup E
inst✝⁹ : NormedAddCommGroup E'
inst✝⁸ : NormedAddCommGroup F
f : G → E
g : G → E'
inst✝⁷ : NontriviallyNormedField 𝕜
inst✝⁶ : NormedSpace 𝕜 E
inst✝⁵ : NormedSpace 𝕜 E'
inst✝⁴ : NormedSpace 𝕜 F
L : E →L[𝕜] E' →L[𝕜] F
inst✝³ : MeasurableSpace G
μ : Measure G
inst✝² : AddGroup G
inst✝¹ : MeasurableAdd G
inst✝ : MeasurableNeg G
x₀ : G
h : ConvolutionExistsAt (fun x => ‖f x‖) (fun x => ‖g x‖) x₀ (mul ℝ ℝ) μ
hmf : AEStronglyMeasurable f μ
hmg : AEStronglyMeasurable g (Measure.map (fun t => x₀ - t) μ)
x : G
⊢ ‖(L (f x)) (g (x₀ - x))‖ ≤ ‖L‖ * (fun x => ‖f x‖) x * (fun x => ‖g x‖) (x₀ - x)

Proof state:
𝕜 : Type u𝕜
G : Type uG
E : Type uE
E' : Type uE'
F : Type uF
inst✝¹⁰ : NormedAddCommGroup E
inst✝⁹ : NormedAddCommGroup E'
inst✝⁸ : NormedAddCommGroup F
f : G → E
g : G → E'
inst✝⁷ : NontriviallyNormedField 𝕜
inst✝⁶ : NormedSpace 𝕜 E
inst✝⁵ : NormedSpace 𝕜 E'
inst✝⁴ : NormedSpace 𝕜 F
L : E →L[𝕜] E' →L[𝕜] F
inst✝³ : MeasurableSpace G
μ : Measure G
inst✝² : AddGroup G
inst✝¹ : MeasurableAdd G
inst✝ : MeasurableNeg G
x₀ : G
h : ConvolutionExistsAt (fun x => ‖f x‖) (fun x => ‖g x‖) x₀ (mul ℝ ℝ) μ
hmf : AEStronglyMeasurable f μ
hmg : AEStronglyMeasurable g (Measure.map (fun t => x₀ - t) μ)
⊢ ConvolutionExistsAt f g x₀ L μ

Tactic:
refine (h.const_mul ‖L‖).mono'
  (hmf.convolution_integrand_snd' L hmg) (Eventually.of_forall fun x => ?_)

Result:
𝕜 : Type u𝕜
G : Type uG
E : Type uE
E' : Type uE'
F : Type uF
inst✝¹⁰ : NormedAddCommGroup E
inst✝⁹ : NormedAddCommGroup E'
inst✝⁸ : NormedAddCommGroup F
f : G → E
g : G → E'
inst✝⁷ : NontriviallyNormedField 𝕜
inst✝⁶ : NormedSpace 𝕜 E
inst✝⁵ : NormedSpace 𝕜 E'
inst✝⁴ : NormedSpace 𝕜 F
L : E →L[𝕜] E' →L[𝕜] F
inst✝³ : MeasurableSpace G
μ : Measure G
inst✝² : AddGroup G
inst✝¹ : MeasurableAdd G
inst✝ : MeasurableNeg G
x₀ : G
h : ConvolutionExistsAt (fun x => ‖f x‖) (fun x => ‖g x‖) x₀ (mul ℝ ℝ) μ
hmf : AEStronglyMeasurable f μ
hmg : AEStronglyMeasurable g (Measure.map (fun t => x₀ - t) μ)
x : G
⊢ ‖(L (f x)) (g (x₀ - x))‖ ≤ ‖L‖ * ((mul ℝ ℝ) ((fun x => ‖f x‖) x)) ((fun x => ‖g x‖) (x₀ - x))