-- Mathlib/MeasureTheory/Integral/SetToL1.lean
theorem continuous_L1_toL1 {μ' : Measure α} (c' : ℝ≥0∞) (hc' : c' ≠ ∞) (hμ'_le : μ' ≤ c' • μ) :
    Continuous fun f : α →₁[μ] G =>
      (Integrable.of_measure_le_smul hc' hμ'_le (L1.integrable_coeFn f)).toL1 f

Proof state:
case h
α : Type u_1
G : Type u_5
inst✝ : NormedAddCommGroup G
m : MeasurableSpace α
μ μ' : Measure α
c' : ℝ≥0∞
hc' : c' ≠ ⊤
hμ'_le : μ' ≤ c' • μ
hc'0 : ¬c' = 0
f : ↥(Lp G 1 μ)
ε : ℝ
hε_pos : ε > 0
g : ↥(Lp G 1 μ)
hfg : (eLpNorm (↑↑g - ↑↑f) 1 μ).toReal < ε / 2 / c'.toReal
h_int : ∀ (f' : ↥(Lp G 1 μ)), Integrable (↑↑f') μ' :=
  fun f' => Integrable.of_measure_le_smul hc' hμ'_le (L1.integrable_coeFn f')
this : eLpNorm (↑↑(Integrable.toL1 ↑↑g ⋯) - ↑↑(Integrable.toL1 ↑↑f ⋯)) 1 μ' = eLpNorm (↑↑g - ↑↑f) 1 μ'
h_eLpNorm_ne_top : eLpNorm (↑↑g - ↑↑f) 1 μ ≠ ⊤
⊢ (eLpNorm (↑↑g - ↑↑f) 1 μ').toReal < ε

Tactic:
calc
  (eLpNorm (⇑g - ⇑f) 1 μ').toReal ≤ (c' * eLpNorm (⇑g - ⇑f) 1 μ).toReal := by
    refine toReal_mono (ENNReal.mul_ne_top hc' h_eLpNorm_ne_top) ?_
    refine (eLpNorm_mono_measure (⇑g - ⇑f) hμ'_le).trans_eq ?_
    rw [eLpNorm_smul_measure_of_ne_zero hc'0, smul_eq_mul]
    simp
  _ = c'.toReal * (eLpNorm (⇑g - ⇑f) 1 μ).toReal := toReal_mul
  _ ≤ c'.toReal * (ε / 2 / c'.toReal) := by gcongr
  _ = ε / 2 := by
    refine mul_div_cancel₀ (ε / 2) ?_; rw [Ne, toReal_eq_zero_iff]; simp [hc', hc'0]
  _ < ε := half_lt_self hε_pos

Result:
no goals

Proof state:
α : Type u_1
G : Type u_5
inst✝ : NormedAddCommGroup G
m : MeasurableSpace α
μ μ' : Measure α
c' : ℝ≥0∞
hc' : c' ≠ ⊤
hμ'_le : μ' ≤ c' • μ
hc'0 : ¬c' = 0
f : ↥(Lp G 1 μ)
ε : ℝ
hε_pos : ε > 0
g : ↥(Lp G 1 μ)
hfg : (eLpNorm (↑↑g - ↑↑f) 1 μ).toReal < ε / 2 / c'.toReal
h_int : ∀ (f' : ↥(Lp G 1 μ)), Integrable (↑↑f') μ' :=
  fun f' => Integrable.of_measure_le_smul hc' hμ'_le (L1.integrable_coeFn f')
this : eLpNorm (↑↑(Integrable.toL1 ↑↑g ⋯) - ↑↑(Integrable.toL1 ↑↑f ⋯)) 1 μ' = eLpNorm (↑↑g - ↑↑f) 1 μ'
h_eLpNorm_ne_top : eLpNorm (↑↑g - ↑↑f) 1 μ ≠ ⊤
⊢ c'.toReal ≠ 0

Tactic:
rw [Ne, toReal_eq_zero_iff]

Result:
α : Type u_1
G : Type u_5
inst✝ : NormedAddCommGroup G
m : MeasurableSpace α
μ μ' : Measure α
c' : ℝ≥0∞
hc' : c' ≠ ⊤
hμ'_le : μ' ≤ c' • μ
hc'0 : ¬c' = 0
f : ↥(Lp G 1 μ)
ε : ℝ
hε_pos : ε > 0
g : ↥(Lp G 1 μ)
hfg : (eLpNorm (↑↑g - ↑↑f) 1 μ).toReal < ε / 2 / c'.toReal
h_int : ∀ (f' : ↥(Lp G 1 μ)), Integrable (↑↑f') μ' :=
  fun f' => Integrable.of_measure_le_smul hc' hμ'_le (L1.integrable_coeFn f')
this : eLpNorm (↑↑(Integrable.toL1 ↑↑g ⋯) - ↑↑(Integrable.toL1 ↑↑f ⋯)) 1 μ' = eLpNorm (↑↑g - ↑↑f) 1 μ'
h_eLpNorm_ne_top : eLpNorm (↑↑g - ↑↑f) 1 μ ≠ ⊤
⊢ ¬(c' = 0 ∨ c' = ⊤)

Proof state:
case pos
α : Type u_1
G : Type u_5
inst✝ : NormedAddCommGroup G
m : MeasurableSpace α
μ μ' : Measure α
c' : ℝ≥0∞
hc' : c' ≠ ⊤
hμ'_le : μ' ≤ c' • μ
hc'0 : c' = 0
hμ'0 : μ' = 0
h_im_zero : (fun f => Integrable.toL1 ↑↑f ⋯) = 0
⊢ Continuous fun f => Integrable.toL1 ↑↑f ⋯

Tactic:
rw [h_im_zero]

Result:
case pos
α : Type u_1
G : Type u_5
inst✝ : NormedAddCommGroup G
m : MeasurableSpace α
μ μ' : Measure α
c' : ℝ≥0∞
hc' : c' ≠ ⊤
hμ'_le : μ' ≤ c' • μ
hc'0 : c' = 0
hμ'0 : μ' = 0
h_im_zero : (fun f => Integrable.toL1 ↑↑f ⋯) = 0
⊢ Continuous 0

Proof state:
case neg
α : Type u_1
G : Type u_5
inst✝ : NormedAddCommGroup G
m : MeasurableSpace α
μ μ' : Measure α
c' : ℝ≥0∞
hc' : c' ≠ ⊤
hμ'_le : μ' ≤ c' • μ
hc'0 : ¬c' = 0
⊢ ∀ (b : ↥(Lp G 1 μ)),
    ∀ ε > 0, ∃ δ > 0, ∀ (a : ↥(Lp G 1 μ)), dist a b < δ → dist (Integrable.toL1 ↑↑a ⋯) (Integrable.toL1 ↑↑b ⋯) < ε

Tactic:
intro f ε hε_pos

Result:
case neg
α : Type u_1
G : Type u_5
inst✝ : NormedAddCommGroup G
m : MeasurableSpace α
μ μ' : Measure α
c' : ℝ≥0∞
hc' : c' ≠ ⊤
hμ'_le : μ' ≤ c' • μ
hc'0 : ¬c' = 0
f : ↥(Lp G 1 μ)
ε : ℝ
hε_pos : ε > 0
⊢ ∃ δ > 0, ∀ (a : ↥(Lp G 1 μ)), dist a f < δ → dist (Integrable.toL1 ↑↑a ⋯) (Integrable.toL1 ↑↑f ⋯) < ε

Proof state:
α : Type u_1
G : Type u_5
inst✝ : NormedAddCommGroup G
m : MeasurableSpace α
μ μ' : Measure α
c' : ℝ≥0∞
hc' : c' ≠ ⊤
hμ'_le : μ' ≤ c' • μ
hc'0 : ¬c' = 0
f : ↥(Lp G 1 μ)
ε : ℝ
hε_pos : ε > 0
g : ↥(Lp G 1 μ)
hfg : (eLpNorm (↑↑g - ↑↑f) 1 μ).toReal < ε / 2 / c'.toReal
h_int : ∀ (f' : ↥(Lp G 1 μ)), Integrable (↑↑f') μ' :=
  fun f' => Integrable.of_measure_le_smul hc' hμ'_le (L1.integrable_coeFn f')
this : eLpNorm (↑↑(Integrable.toL1 ↑↑g ⋯) - ↑↑(Integrable.toL1 ↑↑f ⋯)) 1 μ' = eLpNorm (↑↑g - ↑↑f) 1 μ'
⊢ eLpNorm (↑↑(g - f)) 1 μ ≠ ⊤

Tactic:
exact Lp.eLpNorm_ne_top _

Result:
no goals