-- Mathlib/MeasureTheory/Measure/Doubling.lean
theorem eventually_measure_mul_le_scalingConstantOf_mul (K : ℝ) :
    ∃ R : ℝ,
      0 < R ∧
        ∀ x t r, t ∈ Ioc 0 K → r ≤ R →
          μ (closedBall x (t * r)) ≤ scalingConstantOf μ K * μ (closedBall x r)

Proof state:
case intro.intro.inr.inl
α : Type u_1
inst✝² : PseudoMetricSpace α
inst✝¹ : MeasurableSpace α
μ : Measure α
inst✝ : IsUnifLocDoublingMeasure μ
K : ℝ
h : ∀ᶠ (ε : ℝ) in 𝓝[>] 0, ∀ (x : α), ∀ t ≤ K, μ (closedBall x (t * ε)) ≤ ↑(Classical.choose ⋯) * μ (closedBall x ε)
R : ℝ
Rpos : R ∈ Ioi 0
hR :
  Ioc 0 R ⊆ {x | (fun ε => ∀ (x : α), ∀ t ≤ K, μ (closedBall x (t * ε)) ≤ ↑(Classical.choose ⋯) * μ (closedBall x ε)) x}
x : α
t : ℝ
ht : t ∈ Ioc 0 K
hr : 0 ≤ R
⊢ μ (closedBall x 0) ≤ ↑(scalingConstantOf μ K) * μ (closedBall x 0)

Tactic:
refine le_mul_of_one_le_of_le ?_ le_rfl

Result:
case intro.intro.inr.inl
α : Type u_1
inst✝² : PseudoMetricSpace α
inst✝¹ : MeasurableSpace α
μ : Measure α
inst✝ : IsUnifLocDoublingMeasure μ
K : ℝ
h : ∀ᶠ (ε : ℝ) in 𝓝[>] 0, ∀ (x : α), ∀ t ≤ K, μ (closedBall x (t * ε)) ≤ ↑(Classical.choose ⋯) * μ (closedBall x ε)
R : ℝ
Rpos : R ∈ Ioi 0
hR :
  Ioc 0 R ⊆ {x | (fun ε => ∀ (x : α), ∀ t ≤ K, μ (closedBall x (t * ε)) ≤ ↑(Classical.choose ⋯) * μ (closedBall x ε)) x}
x : α
t : ℝ
ht : t ∈ Ioc 0 K
hr : 0 ≤ R
⊢ 1 ≤ ↑(scalingConstantOf μ K)

Proof state:
case intro.intro.inr.inr
α : Type u_1
inst✝² : PseudoMetricSpace α
inst✝¹ : MeasurableSpace α
μ : Measure α
inst✝ : IsUnifLocDoublingMeasure μ
K : ℝ
h : ∀ᶠ (ε : ℝ) in 𝓝[>] 0, ∀ (x : α), ∀ t ≤ K, μ (closedBall x (t * ε)) ≤ ↑(Classical.choose ⋯) * μ (closedBall x ε)
R : ℝ
Rpos : R ∈ Ioi 0
hR :
  Ioc 0 R ⊆ {x | (fun ε => ∀ (x : α), ∀ t ≤ K, μ (closedBall x (t * ε)) ≤ ↑(Classical.choose ⋯) * μ (closedBall x ε)) x}
x : α
t r : ℝ
ht : t ∈ Ioc 0 K
hr : r ≤ R
rpos : 0 < r
⊢ ↑(Classical.choose ⋯) * μ (closedBall x r) ≤ ↑(scalingConstantOf μ K) * μ (closedBall x r)

Tactic:
gcongr

Result:
case intro.intro.inr.inr.bc.a
α : Type u_1
inst✝² : PseudoMetricSpace α
inst✝¹ : MeasurableSpace α
μ : Measure α
inst✝ : IsUnifLocDoublingMeasure μ
K : ℝ
h : ∀ᶠ (ε : ℝ) in 𝓝[>] 0, ∀ (x : α), ∀ t ≤ K, μ (closedBall x (t * ε)) ≤ ↑(Classical.choose ⋯) * μ (closedBall x ε)
R : ℝ
Rpos : R ∈ Ioi 0
hR :
  Ioc 0 R ⊆ {x | (fun ε => ∀ (x : α), ∀ t ≤ K, μ (closedBall x (t * ε)) ≤ ↑(Classical.choose ⋯) * μ (closedBall x ε)) x}
x : α
t r : ℝ
ht : t ∈ Ioc 0 K
hr : r ≤ R
rpos : 0 < r
⊢ Classical.choose ⋯ ≤ scalingConstantOf μ K

Proof state:
case intro.intro.inl
α : Type u_1
inst✝² : PseudoMetricSpace α
inst✝¹ : MeasurableSpace α
μ : Measure α
inst✝ : IsUnifLocDoublingMeasure μ
K : ℝ
h : ∀ᶠ (ε : ℝ) in 𝓝[>] 0, ∀ (x : α), ∀ t ≤ K, μ (closedBall x (t * ε)) ≤ ↑(Classical.choose ⋯) * μ (closedBall x ε)
R : ℝ
Rpos : R ∈ Ioi 0
hR :
  Ioc 0 R ⊆ {x | (fun ε => ∀ (x : α), ∀ t ≤ K, μ (closedBall x (t * ε)) ≤ ↑(Classical.choose ⋯) * μ (closedBall x ε)) x}
x : α
t r : ℝ
ht : t ∈ Ioc 0 K
hr : r ≤ R
rneg : r < 0
this : t * r < 0
⊢ μ (closedBall x (t * r)) ≤ ↑(scalingConstantOf μ K) * μ (closedBall x r)

Tactic:
simp only [closedBall_eq_empty.2 this, measure_empty, zero_le']

Result:
no goals

Proof state:
case intro.intro.inr.inr
α : Type u_1
inst✝² : PseudoMetricSpace α
inst✝¹ : MeasurableSpace α
μ : Measure α
inst✝ : IsUnifLocDoublingMeasure μ
K : ℝ
h : ∀ᶠ (ε : ℝ) in 𝓝[>] 0, ∀ (x : α), ∀ t ≤ K, μ (closedBall x (t * ε)) ≤ ↑(Classical.choose ⋯) * μ (closedBall x ε)
R : ℝ
Rpos : R ∈ Ioi 0
hR :
  Ioc 0 R ⊆ {x | (fun ε => ∀ (x : α), ∀ t ≤ K, μ (closedBall x (t * ε)) ≤ ↑(Classical.choose ⋯) * μ (closedBall x ε)) x}
x : α
t r : ℝ
ht : t ∈ Ioc 0 K
hr : r ≤ R
rpos : 0 < r
⊢ μ (closedBall x (t * r)) ≤ ↑(scalingConstantOf μ K) * μ (closedBall x r)

Tactic:
apply (hR ⟨rpos, hr⟩ x t ht.2).trans

Result:
case intro.intro.inr.inr
α : Type u_1
inst✝² : PseudoMetricSpace α
inst✝¹ : MeasurableSpace α
μ : Measure α
inst✝ : IsUnifLocDoublingMeasure μ
K : ℝ
h : ∀ᶠ (ε : ℝ) in 𝓝[>] 0, ∀ (x : α), ∀ t ≤ K, μ (closedBall x (t * ε)) ≤ ↑(Classical.choose ⋯) * μ (closedBall x ε)
R : ℝ
Rpos : R ∈ Ioi 0
hR :
  Ioc 0 R ⊆ {x | (fun ε => ∀ (x : α), ∀ t ≤ K, μ (closedBall x (t * ε)) ≤ ↑(Classical.choose ⋯) * μ (closedBall x ε)) x}
x : α
t r : ℝ
ht : t ∈ Ioc 0 K
hr : r ≤ R
rpos : 0 < r
⊢ ↑(Classical.choose ⋯) * μ (closedBall x r) ≤ ↑(scalingConstantOf μ K) * μ (closedBall x r)

Proof state:
case intro.intro.inr.inl
α : Type u_1
inst✝² : PseudoMetricSpace α
inst✝¹ : MeasurableSpace α
μ : Measure α
inst✝ : IsUnifLocDoublingMeasure μ
K : ℝ
h : ∀ᶠ (ε : ℝ) in 𝓝[>] 0, ∀ (x : α), ∀ t ≤ K, μ (closedBall x (t * ε)) ≤ ↑(Classical.choose ⋯) * μ (closedBall x ε)
R : ℝ
Rpos : R ∈ Ioi 0
hR :
  Ioc 0 R ⊆ {x | (fun ε => ∀ (x : α), ∀ t ≤ K, μ (closedBall x (t * ε)) ≤ ↑(Classical.choose ⋯) * μ (closedBall x ε)) x}
x : α
t : ℝ
ht : t ∈ Ioc 0 K
hr : 0 ≤ R
⊢ μ (closedBall x (t * 0)) ≤ ↑(scalingConstantOf μ K) * μ (closedBall x 0)

Tactic:
simp only [mul_zero, closedBall_zero]

Result:
case intro.intro.inr.inl
α : Type u_1
inst✝² : PseudoMetricSpace α
inst✝¹ : MeasurableSpace α
μ : Measure α
inst✝ : IsUnifLocDoublingMeasure μ
K : ℝ
h : ∀ᶠ (ε : ℝ) in 𝓝[>] 0, ∀ (x : α), ∀ t ≤ K, μ (closedBall x (t * ε)) ≤ ↑(Classical.choose ⋯) * μ (closedBall x ε)
R : ℝ
Rpos : R ∈ Ioi 0
hR :
  Ioc 0 R ⊆ {x | (fun ε => ∀ (x : α), ∀ t ≤ K, μ (closedBall x (t * ε)) ≤ ↑(Classical.choose ⋯) * μ (closedBall x ε)) x}
x : α
t : ℝ
ht : t ∈ Ioc 0 K
hr : 0 ≤ R
⊢ μ (closedBall x 0) ≤ ↑(scalingConstantOf μ K) * μ (closedBall x 0)

Proof state:
α : Type u_1
inst✝² : PseudoMetricSpace α
inst✝¹ : MeasurableSpace α
μ : Measure α
inst✝ : IsUnifLocDoublingMeasure μ
K : ℝ
⊢ ∃ R,
    0 < R ∧
      ∀ (x : α) (t r : ℝ),
        t ∈ Ioc 0 K → r ≤ R → μ (closedBall x (t * r)) ≤ ↑(scalingConstantOf μ K) * μ (closedBall x r)

Tactic:
have h := Classical.choose_spec (exists_eventually_forall_measure_closedBall_le_mul μ K)

Result:
α : Type u_1
inst✝² : PseudoMetricSpace α
inst✝¹ : MeasurableSpace α
μ : Measure α
inst✝ : IsUnifLocDoublingMeasure μ
K : ℝ
h : ∀ᶠ (ε : ℝ) in 𝓝[>] 0, ∀ (x : α), ∀ t ≤ K, μ (closedBall x (t * ε)) ≤ ↑(Classical.choose ⋯) * μ (closedBall x ε)
⊢ ∃ R,
    0 < R ∧
      ∀ (x : α) (t r : ℝ),
        t ∈ Ioc 0 K → r ≤ R → μ (closedBall x (t * r)) ≤ ↑(scalingConstantOf μ K) * μ (closedBall x r)