-- Mathlib/MeasureTheory/Integral/BoundedContinuousFunction.lean
lemma norm_integral_le_mul_norm [IsFiniteMeasure μ] (f : X →ᵇ E) :
    ‖∫ x, f x ∂μ‖ ≤ ENNReal.toReal (μ Set.univ) * ‖f‖

Proof state:
X : Type u_1
inst✝⁸ : MeasurableSpace X
inst✝⁷ : TopologicalSpace X
μ : Measure X
E : Type u_2
inst✝⁶ : NormedAddCommGroup E
inst✝⁵ : OpensMeasurableSpace X
inst✝⁴ : SecondCountableTopology E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : NormedSpace ℝ E
inst✝ : IsFiniteMeasure μ
f : X →ᵇ E
⊢ ‖∫ (x : X), f x ∂μ‖ ≤ (μ Set.univ).toReal * ‖f‖

Tactic:
calc  ‖∫ x, f x ∂μ‖
  _ ≤ ∫ x, ‖f x‖ ∂μ                       := by exact norm_integral_le_integral_norm _
  _ ≤ ∫ _, ‖f‖ ∂μ                         := ?_
  _ = ENNReal.toReal (μ Set.univ) • ‖f‖   := by rw [integral_const]

Result:
X : Type u_1
inst✝⁸ : MeasurableSpace X
inst✝⁷ : TopologicalSpace X
μ : Measure X
E : Type u_2
inst✝⁶ : NormedAddCommGroup E
inst✝⁵ : OpensMeasurableSpace X
inst✝⁴ : SecondCountableTopology E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : NormedSpace ℝ E
inst✝ : IsFiniteMeasure μ
f : X →ᵇ E
⊢ ∫ (x : X), ‖f x‖ ∂μ ≤ ∫ (x : X), ‖f‖ ∂μ

Proof state:
X : Type u_1
inst✝⁸ : MeasurableSpace X
inst✝⁷ : TopologicalSpace X
μ : Measure X
E : Type u_2
inst✝⁶ : NormedAddCommGroup E
inst✝⁵ : OpensMeasurableSpace X
inst✝⁴ : SecondCountableTopology E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : NormedSpace ℝ E
inst✝ : IsFiniteMeasure μ
f : X →ᵇ E
⊢ ‖∫ (x : X), f x ∂μ‖ ≤ ∫ (x : X), ‖f x‖ ∂μ

Tactic:
exact norm_integral_le_integral_norm _

Result:
no goals

Proof state:
X : Type u_1
inst✝⁸ : MeasurableSpace X
inst✝⁷ : TopologicalSpace X
μ : Measure X
E : Type u_2
inst✝⁶ : NormedAddCommGroup E
inst✝⁵ : OpensMeasurableSpace X
inst✝⁴ : SecondCountableTopology E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : NormedSpace ℝ E
inst✝ : IsFiniteMeasure μ
f : X →ᵇ E
⊢ ∫ (x : X), ‖f‖ ∂μ = (μ Set.univ).toReal • ‖f‖

Tactic:
rw [integral_const]

Result:
no goals

Proof state:
X : Type u_1
inst✝⁸ : MeasurableSpace X
inst✝⁷ : TopologicalSpace X
μ : Measure X
E : Type u_2
inst✝⁶ : NormedAddCommGroup E
inst✝⁵ : OpensMeasurableSpace X
inst✝⁴ : SecondCountableTopology E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : NormedSpace ℝ E
inst✝ : IsFiniteMeasure μ
f : X →ᵇ E
⊢ ∫ (x : X), ‖f x‖ ∂μ ≤ ∫ (x : X), ‖f‖ ∂μ

Tactic:
apply integral_mono _ (integrable_const ‖f‖) (fun x ↦ f.norm_coe_le_norm x)

Result:
X : Type u_1
inst✝⁸ : MeasurableSpace X
inst✝⁷ : TopologicalSpace X
μ : Measure X
E : Type u_2
inst✝⁶ : NormedAddCommGroup E
inst✝⁵ : OpensMeasurableSpace X
inst✝⁴ : SecondCountableTopology E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : NormedSpace ℝ E
inst✝ : IsFiniteMeasure μ
f : X →ᵇ E
⊢ Integrable (fun x => ‖f x‖) μ

Proof state:
X : Type u_1
inst✝⁸ : MeasurableSpace X
inst✝⁷ : TopologicalSpace X
μ : Measure X
E : Type u_2
inst✝⁶ : NormedAddCommGroup E
inst✝⁵ : OpensMeasurableSpace X
inst✝⁴ : SecondCountableTopology E
inst✝³ : MeasurableSpace E
inst✝² : BorelSpace E
inst✝¹ : NormedSpace ℝ E
inst✝ : IsFiniteMeasure μ
f : X →ᵇ E
⊢ Integrable (fun x => ‖f x‖) μ

Tactic:
exact (integrable_norm_iff f.continuous.measurable.aestronglyMeasurable).mpr (f.integrable μ)

Result:
no goals