-- Mathlib/MeasureTheory/Function/SimpleFuncDenseLp.lean
theorem denseRange_coeSimpleFuncNonnegToLpNonneg [hp : Fact (1 ≤ p)] (hp_ne_top : p ≠ ∞) :
    DenseRange (coeSimpleFuncNonnegToLpNonneg p μ G) := fun g ↦ by
  borelize G
  rw [mem_closure_iff_seq_limit]
  have hg_memLp : MemLp (g : α → G) p μ := Lp.memLp (g : Lp G p μ)
  have zero_mem : (0 : G) ∈ (range (g : α → G) ∪ {0} : Set G) ∩ { y | 0 ≤ y }

Proof state:
case refine_1
α : Type u_1
inst✝¹ : MeasurableSpace α
p : ℝ≥0∞
μ : Measure α
G : Type u_7
inst✝ : NormedLatticeAddCommGroup G
hp : Fact (1 ≤ p)
hp_ne_top : p ≠ ⊤
g : { g // 0 ≤ g }
this✝¹ : MeasurableSpace G := borel G
this✝ : BorelSpace G
hg_memLp : MemLp (↑↑↑g) p μ
zero_mem : 0 ∈ (Set.range ↑↑↑g ∪ {0}) ∩ {y | 0 ≤ y}
this : SeparableSpace ↑((Set.range ↑↑↑g ∪ {0}) ∩ {y | 0 ≤ y})
g_meas : Measurable ↑↑↑g
x : ℕ → α →ₛ G := fun n => SimpleFunc.approxOn (↑↑↑g) g_meas ((Set.range ↑↑↑g ∪ {0}) ∩ {y | 0 ≤ y}) 0 zero_mem n
hx_nonneg : ∀ (n : ℕ), 0 ≤ x n
hx_memLp : ∀ (n : ℕ), MemLp (⇑(x n)) p μ
h_toLp : ∀ (n : ℕ), ↑↑(MemLp.toLp ⇑(x n) ⋯) =ᶠ[ae μ] ⇑(x n)
hx_nonneg_Lp : ∀ (n : ℕ), 0 ≤ toLp (x n) ⋯
hx_tendsto : Tendsto (fun n => eLpNorm (⇑(x n) - ↑↑↑g) p μ) atTop (𝓝 0)
n : ℕ
⊢ ↑↑↑(toLp (x n) ⋯) =ᶠ[ae μ] ⇑(x n)

Tactic:
rw [Lp.simpleFunc.toLp_eq_toLp]

Result:
case refine_1
α : Type u_1
inst✝¹ : MeasurableSpace α
p : ℝ≥0∞
μ : Measure α
G : Type u_7
inst✝ : NormedLatticeAddCommGroup G
hp : Fact (1 ≤ p)
hp_ne_top : p ≠ ⊤
g : { g // 0 ≤ g }
this✝¹ : MeasurableSpace G := borel G
this✝ : BorelSpace G
hg_memLp : MemLp (↑↑↑g) p μ
zero_mem : 0 ∈ (Set.range ↑↑↑g ∪ {0}) ∩ {y | 0 ≤ y}
this : SeparableSpace ↑((Set.range ↑↑↑g ∪ {0}) ∩ {y | 0 ≤ y})
g_meas : Measurable ↑↑↑g
x : ℕ → α →ₛ G := fun n => SimpleFunc.approxOn (↑↑↑g) g_meas ((Set.range ↑↑↑g ∪ {0}) ∩ {y | 0 ≤ y}) 0 zero_mem n
hx_nonneg : ∀ (n : ℕ), 0 ≤ x n
hx_memLp : ∀ (n : ℕ), MemLp (⇑(x n)) p μ
h_toLp : ∀ (n : ℕ), ↑↑(MemLp.toLp ⇑(x n) ⋯) =ᶠ[ae μ] ⇑(x n)
hx_nonneg_Lp : ∀ (n : ℕ), 0 ≤ toLp (x n) ⋯
hx_tendsto : Tendsto (fun n => eLpNorm (⇑(x n) - ↑↑↑g) p μ) atTop (𝓝 0)
n : ℕ
⊢ ↑↑(MemLp.toLp ⇑(x n) ⋯) =ᶠ[ae μ] ⇑(x n)

Proof state:
α : Type u_1
inst✝¹ : MeasurableSpace α
p : ℝ≥0∞
μ : Measure α
G : Type u_7
inst✝ : NormedLatticeAddCommGroup G
hp : Fact (1 ≤ p)
hp_ne_top : p ≠ ⊤
g : { g // 0 ≤ g }
this✝¹ : MeasurableSpace G := borel G
this✝ : BorelSpace G
hg_memLp : MemLp (↑↑↑g) p μ
zero_mem : 0 ∈ (Set.range ↑↑↑g ∪ {0}) ∩ {y | 0 ≤ y}
this : SeparableSpace ↑((Set.range ↑↑↑g ∪ {0}) ∩ {y | 0 ≤ y})
g_meas : Measurable ↑↑↑g
x : ℕ → α →ₛ G := fun n => SimpleFunc.approxOn (↑↑↑g) g_meas ((Set.range ↑↑↑g ∪ {0}) ∩ {y | 0 ≤ y}) 0 zero_mem n
hx_nonneg : ∀ (n : ℕ), 0 ≤ x n
hx_memLp : ∀ (n : ℕ), MemLp (⇑(x n)) p μ
h_toLp : ∀ (n : ℕ), ↑↑(MemLp.toLp ⇑(x n) ⋯) =ᶠ[ae μ] ⇑(x n)
hx_nonneg_Lp : ∀ (n : ℕ), 0 ≤ toLp (x n) ⋯
hx_tendsto : Tendsto (fun n => eLpNorm (⇑(x n) - ↑↑↑g) p μ) atTop (𝓝 0)
⊢ Tendsto (fun n => eLpNorm (↑↑↑(toLp (x n) ⋯) - ↑↑↑g) p μ) atTop (𝓝 0)

Tactic:
refine Filter.Tendsto.congr (fun n => eLpNorm_congr_ae (EventuallyEq.sub ?_ ?_)) hx_tendsto

Result:
case refine_1
α : Type u_1
inst✝¹ : MeasurableSpace α
p : ℝ≥0∞
μ : Measure α
G : Type u_7
inst✝ : NormedLatticeAddCommGroup G
hp : Fact (1 ≤ p)
hp_ne_top : p ≠ ⊤
g : { g // 0 ≤ g }
this✝¹ : MeasurableSpace G := borel G
this✝ : BorelSpace G
hg_memLp : MemLp (↑↑↑g) p μ
zero_mem : 0 ∈ (Set.range ↑↑↑g ∪ {0}) ∩ {y | 0 ≤ y}
this : SeparableSpace ↑((Set.range ↑↑↑g ∪ {0}) ∩ {y | 0 ≤ y})
g_meas : Measurable ↑↑↑g
x : ℕ → α →ₛ G := fun n => SimpleFunc.approxOn (↑↑↑g) g_meas ((Set.range ↑↑↑g ∪ {0}) ∩ {y | 0 ≤ y}) 0 zero_mem n
hx_nonneg : ∀ (n : ℕ), 0 ≤ x n
hx_memLp : ∀ (n : ℕ), MemLp (⇑(x n)) p μ
h_toLp : ∀ (n : ℕ), ↑↑(MemLp.toLp ⇑(x n) ⋯) =ᶠ[ae μ] ⇑(x n)
hx_nonneg_Lp : ∀ (n : ℕ), 0 ≤ toLp (x n) ⋯
hx_tendsto : Tendsto (fun n => eLpNorm (⇑(x n) - ↑↑↑g) p μ) atTop (𝓝 0)
n : ℕ
⊢ ⇑(x n) =ᶠ[ae μ] ↑↑↑(toLp (x n) ⋯)

case refine_2
α : Type u_1
inst✝¹ : MeasurableSpace α
p : ℝ≥0∞
μ : Measure α
G : Type u_7
inst✝ : NormedLatticeAddCommGroup G
hp : Fact (1 ≤ p)
hp_ne_top : p ≠ ⊤
g : { g // 0 ≤ g }
this✝¹ : MeasurableSpace G := borel G
this✝ : BorelSpace G
hg_memLp : MemLp (↑↑↑g) p μ
zero_mem : 0 ∈ (Set.range ↑↑↑g ∪ {0}) ∩ {y | 0 ≤ y}
this : SeparableSpace ↑((Set.range ↑↑↑g ∪ {0}) ∩ {y | 0 ≤ y})
g_meas : Measurable ↑↑↑g
x : ℕ → α →ₛ G := fun n => SimpleFunc.approxOn (↑↑↑g) g_meas ((Set.range ↑↑↑g ∪ {0}) ∩ {y | 0 ≤ y}) 0 zero_mem n
hx_nonneg : ∀ (n : ℕ), 0 ≤ x n
hx_memLp : ∀ (n : ℕ), MemLp (⇑(x n)) p μ
h_toLp : ∀ (n : ℕ), ↑↑(MemLp.toLp ⇑(x n) ⋯) =ᶠ[ae μ] ⇑(x n)
hx_nonneg_Lp : ∀ (n : ℕ), 0 ≤ toLp (x n) ⋯
hx_tendsto : Tendsto (fun n => eLpNorm (⇑(x n) - ↑↑↑g) p μ) atTop (𝓝 0)
n : ℕ
⊢ ↑↑↑g =ᶠ[ae μ] ↑↑↑g

Proof state:
case hμ
α : Type u_1
inst✝¹ : MeasurableSpace α
p : ℝ≥0∞
μ : Measure α
G : Type u_7
inst✝ : NormedLatticeAddCommGroup G
hp : Fact (1 ≤ p)
hp_ne_top : p ≠ ⊤
g : { g // 0 ≤ g }
this✝¹ : MeasurableSpace G := borel G
this✝ : BorelSpace G
hg_memLp : MemLp (↑↑↑g) p μ
zero_mem : 0 ∈ (Set.range ↑↑↑g ∪ {0}) ∩ {y | 0 ≤ y}
this : SeparableSpace ↑((Set.range ↑↑↑g ∪ {0}) ∩ {y | 0 ≤ y})
g_meas : Measurable ↑↑↑g
x : ℕ → α →ₛ G := fun n => SimpleFunc.approxOn (↑↑↑g) g_meas ((Set.range ↑↑↑g ∪ {0}) ∩ {y | 0 ≤ y}) 0 zero_mem n
hx_nonneg : ∀ (n : ℕ), 0 ≤ x n
hx_memLp : ∀ (n : ℕ), MemLp (⇑(x n)) p μ
h_toLp : ∀ (n : ℕ), ↑↑(MemLp.toLp ⇑(x n) ⋯) =ᶠ[ae μ] ⇑(x n)
hx_nonneg_Lp : ∀ (n : ℕ), 0 ≤ toLp (x n) ⋯
hg_nonneg : 0 ≤ᶠ[ae μ] ↑↑↑g
a : α
ha : 0 a ≤ ↑↑↑g a
⊢ ↑↑↑g a ∈ (Set.range ↑↑↑g ∪ {0}) ∩ {y | 0 ≤ y}

Tactic:
simpa using ha

Result:
no goals

Proof state:
α : Type u_1
inst✝¹ : MeasurableSpace α
p : ℝ≥0∞
μ : Measure α
G : Type u_7
inst✝ : NormedLatticeAddCommGroup G
hp : Fact (1 ≤ p)
hp_ne_top : p ≠ ⊤
g : { g // 0 ≤ g }
this✝¹ : MeasurableSpace G := borel G
this✝ : BorelSpace G
⊢ g ∈ closure (Set.range (coeSimpleFuncNonnegToLpNonneg p μ G))

Tactic:
rw [mem_closure_iff_seq_limit]

Result:
α : Type u_1
inst✝¹ : MeasurableSpace α
p : ℝ≥0∞
μ : Measure α
G : Type u_7
inst✝ : NormedLatticeAddCommGroup G
hp : Fact (1 ≤ p)
hp_ne_top : p ≠ ⊤
g : { g // 0 ≤ g }
this✝¹ : MeasurableSpace G := borel G
this✝ : BorelSpace G
⊢ ∃ x, (∀ (n : ℕ), x n ∈ Set.range (coeSimpleFuncNonnegToLpNonneg p μ G)) ∧ Tendsto x atTop (𝓝 g)