-- Mathlib/MeasureTheory/OuterMeasure/Induced.lean
theorem inducedOuterMeasure_exists_set {s : Set α} (hs : inducedOuterMeasure m P0 m0 s ≠ ∞)
    {ε : ℝ≥0∞} (hε : ε ≠ 0) :
    ∃ t : Set α,
      P t ∧ s ⊆ t ∧ inducedOuterMeasure m P0 m0 t ≤ inducedOuterMeasure m P0 m0 s + ε

Proof state:
α : Type u_1
P : Set α → Prop
m : (s : Set α) → P s → ℝ≥0∞
P0 : P ∅
m0 : m ∅ P0 = 0
PU : ∀ ⦃f : ℕ → Set α⦄, (∀ (i : ℕ), P (f i)) → P (⋃ i, f i)
msU : ∀ ⦃f : ℕ → Set α⦄ (hm : ∀ (i : ℕ), P (f i)), m (⋃ i, f i) ⋯ ≤ ∑' (i : ℕ), m (f i) ⋯
m_mono : ∀ ⦃s₁ s₂ : Set α⦄ (hs₁ : P s₁) (hs₂ : P s₂), s₁ ⊆ s₂ → m s₁ hs₁ ≤ m s₂ hs₂
s : Set α
hs : (inducedOuterMeasure m P0 m0) s ≠ ⊤
ε : ℝ≥0∞
hε : ε ≠ 0
⊢ ∃ t, P t ∧ s ⊆ t ∧ (inducedOuterMeasure m P0 m0) t ≤ (inducedOuterMeasure m P0 m0) s + ε

Tactic:
have h := ENNReal.lt_add_right hs hε

Result:
α : Type u_1
P : Set α → Prop
m : (s : Set α) → P s → ℝ≥0∞
P0 : P ∅
m0 : m ∅ P0 = 0
PU : ∀ ⦃f : ℕ → Set α⦄, (∀ (i : ℕ), P (f i)) → P (⋃ i, f i)
msU : ∀ ⦃f : ℕ → Set α⦄ (hm : ∀ (i : ℕ), P (f i)), m (⋃ i, f i) ⋯ ≤ ∑' (i : ℕ), m (f i) ⋯
m_mono : ∀ ⦃s₁ s₂ : Set α⦄ (hs₁ : P s₁) (hs₂ : P s₂), s₁ ⊆ s₂ → m s₁ hs₁ ≤ m s₂ hs₂
s : Set α
hs : (inducedOuterMeasure m P0 m0) s ≠ ⊤
ε : ℝ≥0∞
hε : ε ≠ 0
h : (inducedOuterMeasure m P0 m0) s < (inducedOuterMeasure m P0 m0) s + ε
⊢ ∃ t, P t ∧ s ⊆ t ∧ (inducedOuterMeasure m P0 m0) t ≤ (inducedOuterMeasure m P0 m0) s + ε

Proof state:
α : Type u_1
P : Set α → Prop
m : (s : Set α) → P s → ℝ≥0∞
P0 : P ∅
m0 : m ∅ P0 = 0
PU : ∀ ⦃f : ℕ → Set α⦄, (∀ (i : ℕ), P (f i)) → P (⋃ i, f i)
msU : ∀ ⦃f : ℕ → Set α⦄ (hm : ∀ (i : ℕ), P (f i)), m (⋃ i, f i) ⋯ ≤ ∑' (i : ℕ), m (f i) ⋯
m_mono : ∀ ⦃s₁ s₂ : Set α⦄ (hs₁ : P s₁) (hs₂ : P s₂), s₁ ⊆ s₂ → m s₁ hs₁ ≤ m s₂ hs₂
s : Set α
hs : (inducedOuterMeasure m P0 m0) s ≠ ⊤
ε : ℝ≥0∞
hε : ε ≠ 0
h : (inducedOuterMeasure m P0 m0) s < (inducedOuterMeasure m P0 m0) s + ε
⊢ ∃ t, P t ∧ s ⊆ t ∧ (inducedOuterMeasure m P0 m0) t ≤ (inducedOuterMeasure m P0 m0) s + ε

Tactic:
conv at h =>
  lhs
  rw [inducedOuterMeasure_eq_iInf _ msU m_mono]

Result:
α : Type u_1
P : Set α → Prop
m : (s : Set α) → P s → ℝ≥0∞
P0 : P ∅
m0 : m ∅ P0 = 0
PU : ∀ ⦃f : ℕ → Set α⦄, (∀ (i : ℕ), P (f i)) → P (⋃ i, f i)
msU : ∀ ⦃f : ℕ → Set α⦄ (hm : ∀ (i : ℕ), P (f i)), m (⋃ i, f i) ⋯ ≤ ∑' (i : ℕ), m (f i) ⋯
m_mono : ∀ ⦃s₁ s₂ : Set α⦄ (hs₁ : P s₁) (hs₂ : P s₂), s₁ ⊆ s₂ → m s₁ hs₁ ≤ m s₂ hs₂
s : Set α
hs : (inducedOuterMeasure m P0 m0) s ≠ ⊤
ε : ℝ≥0∞
hε : ε ≠ 0
h : ⨅ t, ⨅ (ht : P t), ⨅ (_ : s ⊆ t), m t ht < (inducedOuterMeasure m P0 m0) s + ε
⊢ ∃ t, P t ∧ s ⊆ t ∧ (inducedOuterMeasure m P0 m0) t ≤ (inducedOuterMeasure m P0 m0) s + ε

Proof state:
case intro.intro.intro
α : Type u_1
P : Set α → Prop
m : (s : Set α) → P s → ℝ≥0∞
P0 : P ∅
m0 : m ∅ P0 = 0
PU : ∀ ⦃f : ℕ → Set α⦄, (∀ (i : ℕ), P (f i)) → P (⋃ i, f i)
msU : ∀ ⦃f : ℕ → Set α⦄ (hm : ∀ (i : ℕ), P (f i)), m (⋃ i, f i) ⋯ ≤ ∑' (i : ℕ), m (f i) ⋯
m_mono : ∀ ⦃s₁ s₂ : Set α⦄ (hs₁ : P s₁) (hs₂ : P s₂), s₁ ⊆ s₂ → m s₁ hs₁ ≤ m s₂ hs₂
s : Set α
hs : (inducedOuterMeasure m P0 m0) s ≠ ⊤
ε : ℝ≥0∞
hε : ε ≠ 0
t : Set α
h1t : P t
h2t : s ⊆ t
h3t : m t ⋯ < (inducedOuterMeasure m P0 m0) s + ε
⊢ ∃ t, P t ∧ s ⊆ t ∧ (inducedOuterMeasure m P0 m0) t ≤ (inducedOuterMeasure m P0 m0) s + ε

Tactic:
exact
  ⟨t, h1t, h2t, le_trans (le_of_eq <| inducedOuterMeasure_eq' _ msU m_mono h1t) (le_of_lt h3t)⟩

Result:
no goals

Proof state:
α : Type u_1
P : Set α → Prop
m : (s : Set α) → P s → ℝ≥0∞
P0 : P ∅
m0 : m ∅ P0 = 0
PU : ∀ ⦃f : ℕ → Set α⦄, (∀ (i : ℕ), P (f i)) → P (⋃ i, f i)
msU : ∀ ⦃f : ℕ → Set α⦄ (hm : ∀ (i : ℕ), P (f i)), m (⋃ i, f i) ⋯ ≤ ∑' (i : ℕ), m (f i) ⋯
m_mono : ∀ ⦃s₁ s₂ : Set α⦄ (hs₁ : P s₁) (hs₂ : P s₂), s₁ ⊆ s₂ → m s₁ hs₁ ≤ m s₂ hs₂
s : Set α
hs : (inducedOuterMeasure m P0 m0) s ≠ ⊤
ε : ℝ≥0∞
hε : ε ≠ 0
h : ∃ i, ∃ (h : P i) (_ : s ⊆ i), m i ⋯ < (inducedOuterMeasure m P0 m0) s + ε
⊢ ∃ t, P t ∧ s ⊆ t ∧ (inducedOuterMeasure m P0 m0) t ≤ (inducedOuterMeasure m P0 m0) s + ε

Tactic:
rcases h with ⟨t, h1t, h2t, h3t⟩

Result:
case intro.intro.intro
α : Type u_1
P : Set α → Prop
m : (s : Set α) → P s → ℝ≥0∞
P0 : P ∅
m0 : m ∅ P0 = 0
PU : ∀ ⦃f : ℕ → Set α⦄, (∀ (i : ℕ), P (f i)) → P (⋃ i, f i)
msU : ∀ ⦃f : ℕ → Set α⦄ (hm : ∀ (i : ℕ), P (f i)), m (⋃ i, f i) ⋯ ≤ ∑' (i : ℕ), m (f i) ⋯
m_mono : ∀ ⦃s₁ s₂ : Set α⦄ (hs₁ : P s₁) (hs₂ : P s₂), s₁ ⊆ s₂ → m s₁ hs₁ ≤ m s₂ hs₂
s : Set α
hs : (inducedOuterMeasure m P0 m0) s ≠ ⊤
ε : ℝ≥0∞
hε : ε ≠ 0
t : Set α
h1t : P t
h2t : s ⊆ t
h3t : m t ⋯ < (inducedOuterMeasure m P0 m0) s + ε
⊢ ∃ t, P t ∧ s ⊆ t ∧ (inducedOuterMeasure m P0 m0) t ≤ (inducedOuterMeasure m P0 m0) s + ε

Proof state:
α : Type u_1
P : Set α → Prop
m : (s : Set α) → P s → ℝ≥0∞
P0 : P ∅
m0 : m ∅ P0 = 0
PU : ∀ ⦃f : ℕ → Set α⦄, (∀ (i : ℕ), P (f i)) → P (⋃ i, f i)
msU : ∀ ⦃f : ℕ → Set α⦄ (hm : ∀ (i : ℕ), P (f i)), m (⋃ i, f i) ⋯ ≤ ∑' (i : ℕ), m (f i) ⋯
m_mono : ∀ ⦃s₁ s₂ : Set α⦄ (hs₁ : P s₁) (hs₂ : P s₂), s₁ ⊆ s₂ → m s₁ hs₁ ≤ m s₂ hs₂
s : Set α
hs : (inducedOuterMeasure m P0 m0) s ≠ ⊤
ε : ℝ≥0∞
hε : ε ≠ 0
h : ⨅ t, ⨅ (ht : P t), ⨅ (_ : s ⊆ t), m t ht < (inducedOuterMeasure m P0 m0) s + ε
⊢ ∃ t, P t ∧ s ⊆ t ∧ (inducedOuterMeasure m P0 m0) t ≤ (inducedOuterMeasure m P0 m0) s + ε

Tactic:
simp only [iInf_lt_iff] at h

Result:
α : Type u_1
P : Set α → Prop
m : (s : Set α) → P s → ℝ≥0∞
P0 : P ∅
m0 : m ∅ P0 = 0
PU : ∀ ⦃f : ℕ → Set α⦄, (∀ (i : ℕ), P (f i)) → P (⋃ i, f i)
msU : ∀ ⦃f : ℕ → Set α⦄ (hm : ∀ (i : ℕ), P (f i)), m (⋃ i, f i) ⋯ ≤ ∑' (i : ℕ), m (f i) ⋯
m_mono : ∀ ⦃s₁ s₂ : Set α⦄ (hs₁ : P s₁) (hs₂ : P s₂), s₁ ⊆ s₂ → m s₁ hs₁ ≤ m s₂ hs₂
s : Set α
hs : (inducedOuterMeasure m P0 m0) s ≠ ⊤
ε : ℝ≥0∞
hε : ε ≠ 0
h : ∃ i, ∃ (h : P i) (_ : s ⊆ i), m i ⋯ < (inducedOuterMeasure m P0 m0) s + ε
⊢ ∃ t, P t ∧ s ⊆ t ∧ (inducedOuterMeasure m P0 m0) t ≤ (inducedOuterMeasure m P0 m0) s + ε