-- Mathlib/MeasureTheory/Function/L2Space.lean
theorem norm_sq_eq_inner' (f : α →₂[μ] E) : ‖f‖ ^ 2 = RCLike.re ⟪f, f⟫

Proof state:
α : Type u_1
E : Type u_2
𝕜 : Type u_4
inst✝³ : RCLike 𝕜
inst✝² : MeasurableSpace α
μ : Measure α
inst✝¹ : NormedAddCommGroup E
inst✝ : InnerProductSpace 𝕜 E
f : ↥(Lp E 2 μ)
h_two : ENNReal.toReal 2 = 2
⊢ ‖f‖ ^ 2 = RCLike.re (inner f f)

Tactic:
rw [inner_def, integral_inner_eq_sq_eLpNorm, norm_def, ← ENNReal.toReal_pow, RCLike.ofReal_re,
  ENNReal.toReal_eq_toReal (ENNReal.pow_ne_top (Lp.eLpNorm_ne_top f)) _]

Result:
α : Type u_1
E : Type u_2
𝕜 : Type u_4
inst✝³ : RCLike 𝕜
inst✝² : MeasurableSpace α
μ : Measure α
inst✝¹ : NormedAddCommGroup E
inst✝ : InnerProductSpace 𝕜 E
f : ↥(Lp E 2 μ)
h_two : ENNReal.toReal 2 = 2
⊢ eLpNorm (↑↑f) 2 μ ^ 2 = ∫⁻ (a : α), ↑‖↑↑f a‖₊ ^ 2 ∂μ

α : Type u_1
E : Type u_2
𝕜 : Type u_4
inst✝³ : RCLike 𝕜
inst✝² : MeasurableSpace α
μ : Measure α
inst✝¹ : NormedAddCommGroup E
inst✝ : InnerProductSpace 𝕜 E
f : ↥(Lp E 2 μ)
h_two : ENNReal.toReal 2 = 2
⊢ ∫⁻ (a : α), ↑‖↑↑f a‖₊ ^ 2 ∂μ ≠ ⊤

Proof state:
α : Type u_1
E : Type u_2
𝕜 : Type u_4
inst✝³ : RCLike 𝕜
inst✝² : MeasurableSpace α
μ : Measure α
inst✝¹ : NormedAddCommGroup E
inst✝ : InnerProductSpace 𝕜 E
f : ↥(Lp E 2 μ)
⊢ ENNReal.toReal 2 = 2

Tactic:
simp

Result:
no goals

Proof state:
α : Type u_1
E : Type u_2
𝕜 : Type u_4
inst✝³ : RCLike 𝕜
inst✝² : MeasurableSpace α
μ : Measure α
inst✝¹ : NormedAddCommGroup E
inst✝ : InnerProductSpace 𝕜 E
f : ↥(Lp E 2 μ)
h_two : ENNReal.toReal 2 = 2
⊢ (∫⁻ (a : α), ‖↑↑f a‖ₑ ^ 2 ∂μ) ^ (2⁻¹ * ↑2) = ∫⁻ (a : α), ↑‖↑↑f a‖₊ ^ 2 ∂μ

Tactic:
simp [enorm_eq_nnnorm]

Result:
no goals

Proof state:
α : Type u_1
E : Type u_2
𝕜 : Type u_4
inst✝³ : RCLike 𝕜
inst✝² : MeasurableSpace α
μ : Measure α
inst✝¹ : NormedAddCommGroup E
inst✝ : InnerProductSpace 𝕜 E
f : ↥(Lp E 2 μ)
h_two : ENNReal.toReal 2 = 2
⊢ ∫⁻ (a : α), ↑‖↑↑f a‖₊ ^ 2 ∂μ ≠ ⊤

Tactic:
refine (lintegral_rpow_enorm_lt_top_of_eLpNorm'_lt_top zero_lt_two (ε := E) ?_).ne

Result:
α : Type u_1
E : Type u_2
𝕜 : Type u_4
inst✝³ : RCLike 𝕜
inst✝² : MeasurableSpace α
μ : Measure α
inst✝¹ : NormedAddCommGroup E
inst✝ : InnerProductSpace 𝕜 E
f : ↥(Lp E 2 μ)
h_two : ENNReal.toReal 2 = 2
⊢ eLpNorm' (↑↑f) 2 μ < ⊤

Proof state:
α : Type u_1
E : Type u_2
𝕜 : Type u_4
inst✝³ : RCLike 𝕜
inst✝² : MeasurableSpace α
μ : Measure α
inst✝¹ : NormedAddCommGroup E
inst✝ : InnerProductSpace 𝕜 E
f : ↥(Lp E 2 μ)
⊢ ‖f‖ ^ 2 = RCLike.re (inner f f)

Tactic:
have h_two : (2 : ℝ≥0∞).toReal = 2 := by simp

Result:
α : Type u_1
E : Type u_2
𝕜 : Type u_4
inst✝³ : RCLike 𝕜
inst✝² : MeasurableSpace α
μ : Measure α
inst✝¹ : NormedAddCommGroup E
inst✝ : InnerProductSpace 𝕜 E
f : ↥(Lp E 2 μ)
h_two : ENNReal.toReal 2 = 2
⊢ ‖f‖ ^ 2 = RCLike.re (inner f f)

Proof state:
α : Type u_1
E : Type u_2
𝕜 : Type u_4
inst✝³ : RCLike 𝕜
inst✝² : MeasurableSpace α
μ : Measure α
inst✝¹ : NormedAddCommGroup E
inst✝ : InnerProductSpace 𝕜 E
f : ↥(Lp E 2 μ)
h_two : ENNReal.toReal 2 = 2
⊢ eLpNorm (↑↑f) 2 μ ^ 2 = ∫⁻ (a : α), ↑‖↑↑f a‖₊ ^ 2 ∂μ

Tactic:
rw [← ENNReal.rpow_natCast, eLpNorm_eq_eLpNorm' two_ne_zero ENNReal.ofNat_ne_top, eLpNorm', ←
  ENNReal.rpow_mul, one_div, h_two]

Result:
α : Type u_1
E : Type u_2
𝕜 : Type u_4
inst✝³ : RCLike 𝕜
inst✝² : MeasurableSpace α
μ : Measure α
inst✝¹ : NormedAddCommGroup E
inst✝ : InnerProductSpace 𝕜 E
f : ↥(Lp E 2 μ)
h_two : ENNReal.toReal 2 = 2
⊢ (∫⁻ (a : α), ‖↑↑f a‖ₑ ^ 2 ∂μ) ^ (2⁻¹ * ↑2) = ∫⁻ (a : α), ↑‖↑↑f a‖₊ ^ 2 ∂μ

Proof state:
α : Type u_1
E : Type u_2
𝕜 : Type u_4
inst✝³ : RCLike 𝕜
inst✝² : MeasurableSpace α
μ : Measure α
inst✝¹ : NormedAddCommGroup E
inst✝ : InnerProductSpace 𝕜 E
f : ↥(Lp E 2 μ)
h_two : ENNReal.toReal 2 = 2
⊢ eLpNorm (↑↑f) 2 μ < ⊤

Tactic:
exact Lp.eLpNorm_lt_top f

Result:
no goals

Proof state:
α : Type u_1
E : Type u_2
𝕜 : Type u_4
inst✝³ : RCLike 𝕜
inst✝² : MeasurableSpace α
μ : Measure α
inst✝¹ : NormedAddCommGroup E
inst✝ : InnerProductSpace 𝕜 E
f : ↥(Lp E 2 μ)
h_two : ENNReal.toReal 2 = 2
⊢ eLpNorm' (↑↑f) 2 μ < ⊤

Tactic:
rw [← h_two, ← eLpNorm_eq_eLpNorm' two_ne_zero ENNReal.ofNat_ne_top]

Result:
α : Type u_1
E : Type u_2
𝕜 : Type u_4
inst✝³ : RCLike 𝕜
inst✝² : MeasurableSpace α
μ : Measure α
inst✝¹ : NormedAddCommGroup E
inst✝ : InnerProductSpace 𝕜 E
f : ↥(Lp E 2 μ)
h_two : ENNReal.toReal 2 = 2
⊢ eLpNorm (↑↑f) 2 μ < ⊤