l3lab/ntp-mathlib huggingface dataset:
/-- A property holds for all polynomials of non-zero `natDegree` with coefficients in a
semiring `R` if it holds for
* `p + a`, with `a ∈ R`, `p ∈ R[X]`,
* `p + q`, with `p, q ∈ R[X]`,
* monomials with nonzero coefficient and non-zero exponent,
with appropriate restrictions on each term.
Note that multiplication is "hidden" in the assumption on monomials, so there is no explicit
multiplication in the statement.
See `degree_pos_induction_on` for a similar statement involving more explicit multiplications.
 -/
@[elab_as_elim]
theorem natDegree_ne_zero_induction_on {M : R[X] → Prop} {f : R[X]} (f0 : f.natDegree ≠ 0)
    (h_C_add : ∀ {a p}, M p → M (C a + p)) (h_add : ∀ {p q}, M p → M q → M (p + q))
    (h_monomial : ∀ {n : ℕ} {a : R}, a ≠ 0 → n ≠ 0 → M (monomial n a)) : M f := by
  suffices f.natDegree = 0 ∨ M f from Or.recOn this (fun h => (f0 h).elim) id
  refine Polynomial.induction_on f ?_ ?_ ?_
  · exact fun a => Or.inl (natDegree_C _)
  · rintro p q (hp | hp) (hq | hq)
    · refine' Or.inl _
      rw [eq_C_of_natDegree_eq_zero hp, eq_C_of_natDegree_eq_zero hq, ← C_add, natDegree_C]
    · refine' Or.inr _
      rw [eq_C_of_natDegree_eq_zero hp]
      exact h_C_add hq
    · refine' Or.inr _
      rw [eq_C_of_natDegree_eq_zero hq, add_comm]
      exact h_C_add hp
    · exact Or.inr (h_add hp hq)
  · intro n a _
    

Proof state:
case refine_3
R : Type u
S : Type v
T : Type w
A : Type z
a✝¹ b : R
n✝ : ℕ
inst✝ : Semiring R
p q : R[X]
M : R[X] → Prop
f : R[X]
f0 : natDegree f ≠ 0
h_C_add : ∀ {a : R} {p : R[X]}, M p → M (C a + p)
h_add : ∀ {p q : R[X]}, M p → M q → M (p + q)
h_monomial : ∀ {n : ℕ} {a : R}, a ≠ 0 → n ≠ 0 → M ((monomial n) a)
n : ℕ
a : R
a✝ : natDegree (C a * X ^ n) = 0 ∨ M (C a * X ^ n)
⊢ natDegree (C a * X ^ (n + 1)) = 0 ∨ M (C a * X ^ (n + 1))

Next tactic:
by_cases a0 : a = 0
/-- A property holds for all polynomials of non-zero `natDegree` with coefficients in a
semiring `R` if it holds for
* `p + a`, with `a ∈ R`, `p ∈ R[X]`,
* `p + q`, with `p, q ∈ R[X]`,
* monomials with nonzero coefficient and non-zero exponent,
with appropriate restrictions on each term.
Note that multiplication is "hidden" in the assumption on monomials, so there is no explicit
multiplication in the statement.
See `degree_pos_induction_on` for a similar statement involving more explicit multiplications.
 -/
@[elab_as_elim]
theorem natDegree_ne_zero_induction_on {M : R[X] → Prop} {f : R[X]} (f0 : f.natDegree ≠ 0)
    (h_C_add : ∀ {a p}, M p → M (C a + p)) (h_add : ∀ {p q}, M p → M q → M (p + q))
    (h_monomial : ∀ {n : ℕ} {a : R}, a ≠ 0 → n ≠ 0 → M (monomial n a)) : M f := by
  suffices f.natDegree = 0 ∨ M f from Or.recOn this (fun h => (f0 h).elim) id
  refine Polynomial.induction_on f ?_ ?_ ?_
  · exact fun a => Or.inl (natDegree_C _)
  · rintro p q (hp | hp) (hq | hq)
    · refine' Or.inl _
      rw [eq_C_of_natDegree_eq_zero hp, eq_C_of_natDegree_eq_zero hq, ← C_add, natDegree_C]
    · refine' Or.inr _
      rw [eq_C_of_natDegree_eq_zero hp]
      exact h_C_add hq
    · refine' Or.inr _
      rw [eq_C_of_natDegree_eq_zero hq, add_comm]
      exact h_C_add hp
    · exact Or.inr (h_add hp hq)
  · intro n a _
    by_cases a0 : a = 0
    · 

Proof state:
case pos
R : Type u
S : Type v
T : Type w
A : Type z
a✝¹ b : R
n✝ : ℕ
inst✝ : Semiring R
p q : R[X]
M : R[X] → Prop
f : R[X]
f0 : natDegree f ≠ 0
h_C_add : ∀ {a : R} {p : R[X]}, M p → M (C a + p)
h_add : ∀ {p q : R[X]}, M p → M q → M (p + q)
h_monomial : ∀ {n : ℕ} {a : R}, a ≠ 0 → n ≠ 0 → M ((monomial n) a)
n : ℕ
a : R
a✝ : natDegree (C a * X ^ n) = 0 ∨ M (C a * X ^ n)
a0 : a = 0
⊢ natDegree (C a * X ^ (n + 1)) = 0 ∨ M (C a * X ^ (n + 1))

Next tactic:
exact Or.inl (by rw [a0, C_0, zero_mul, natDegree_zero])
/-- A property holds for all polynomials of non-zero `natDegree` with coefficients in a
semiring `R` if it holds for
* `p + a`, with `a ∈ R`, `p ∈ R[X]`,
* `p + q`, with `p, q ∈ R[X]`,
* monomials with nonzero coefficient and non-zero exponent,
with appropriate restrictions on each term.
Note that multiplication is "hidden" in the assumption on monomials, so there is no explicit
multiplication in the statement.
See `degree_pos_induction_on` for a similar statement involving more explicit multiplications.
 -/
@[elab_as_elim]
theorem natDegree_ne_zero_induction_on {M : R[X] → Prop} {f : R[X]} (f0 : f.natDegree ≠ 0)
    (h_C_add : ∀ {a p}, M p → M (C a + p)) (h_add : ∀ {p q}, M p → M q → M (p + q))
    (h_monomial : ∀ {n : ℕ} {a : R}, a ≠ 0 → n ≠ 0 → M (monomial n a)) : M f := by
  suffices f.natDegree = 0 ∨ M f from Or.recOn this (fun h => (f0 h).elim) id
  refine Polynomial.induction_on f ?_ ?_ ?_
  · exact fun a => Or.inl (natDegree_C _)
  · rintro p q (hp | hp) (hq | hq)
    · refine' Or.inl _
      rw [eq_C_of_natDegree_eq_zero hp, eq_C_of_natDegree_eq_zero hq, ← C_add, natDegree_C]
    · refine' Or.inr _
      rw [eq_C_of_natDegree_eq_zero hp]
      exact h_C_add hq
    · refine' Or.inr _
      rw [eq_C_of_natDegree_eq_zero hq, add_comm]
      exact h_C_add hp
    · exact Or.inr (h_add hp hq)
  · intro n a _
    by_cases a0 : a = 0
    · exact Or.inl (by 

Proof state:
R : Type u
S : Type v
T : Type w
A : Type z
a✝¹ b : R
n✝ : ℕ
inst✝ : Semiring R
p q : R[X]
M : R[X] → Prop
f : R[X]
f0 : natDegree f ≠ 0
h_C_add : ∀ {a : R} {p : R[X]}, M p → M (C a + p)
h_add : ∀ {p q : R[X]}, M p → M q → M (p + q)
h_monomial : ∀ {n : ℕ} {a : R}, a ≠ 0 → n ≠ 0 → M ((monomial n) a)
n : ℕ
a : R
a✝ : natDegree (C a * X ^ n) = 0 ∨ M (C a * X ^ n)
a0 : a = 0
⊢ natDegree (C a * X ^ (n + 1)) = 0

Next tactic:
rw [a0, C_0, zero_mul, natDegree_zero]
/-- A property holds for all polynomials of non-zero `natDegree` with coefficients in a
semiring `R` if it holds for
* `p + a`, with `a ∈ R`, `p ∈ R[X]`,
* `p + q`, with `p, q ∈ R[X]`,
* monomials with nonzero coefficient and non-zero exponent,
with appropriate restrictions on each term.
Note that multiplication is "hidden" in the assumption on monomials, so there is no explicit
multiplication in the statement.
See `degree_pos_induction_on` for a similar statement involving more explicit multiplications.
 -/
@[elab_as_elim]
theorem natDegree_ne_zero_induction_on {M : R[X] → Prop} {f : R[X]} (f0 : f.natDegree ≠ 0)
    (h_C_add : ∀ {a p}, M p → M (C a + p)) (h_add : ∀ {p q}, M p → M q → M (p + q))
    (h_monomial : ∀ {n : ℕ} {a : R}, a ≠ 0 → n ≠ 0 → M (monomial n a)) : M f := by
  suffices f.natDegree = 0 ∨ M f from Or.recOn this (fun h => (f0 h).elim) id
  refine Polynomial.induction_on f ?_ ?_ ?_
  · exact fun a => Or.inl (natDegree_C _)
  · rintro p q (hp | hp) (hq | hq)
    · refine' Or.inl _
      rw [eq_C_of_natDegree_eq_zero hp, eq_C_of_natDegree_eq_zero hq, ← C_add, natDegree_C]
    · refine' Or.inr _
      rw [eq_C_of_natDegree_eq_zero hp]
      exact h_C_add hq
    · refine' Or.inr _
      rw [eq_C_of_natDegree_eq_zero hq, add_comm]
      exact h_C_add hp
    · exact Or.inr (h_add hp hq)
  · intro n a _
    by_cases a0 : a = 0
    · exact Or.inl (by rw [a0, C_0, zero_mul, natDegree_zero])
    · 

Proof state:
case neg
R : Type u
S : Type v
T : Type w
A : Type z
a✝¹ b : R
n✝ : ℕ
inst✝ : Semiring R
p q : R[X]
M : R[X] → Prop
f : R[X]
f0 : natDegree f ≠ 0
h_C_add : ∀ {a : R} {p : R[X]}, M p → M (C a + p)
h_add : ∀ {p q : R[X]}, M p → M q → M (p + q)
h_monomial : ∀ {n : ℕ} {a : R}, a ≠ 0 → n ≠ 0 → M ((monomial n) a)
n : ℕ
a : R
a✝ : natDegree (C a * X ^ n) = 0 ∨ M (C a * X ^ n)
a0 : ¬a = 0
⊢ natDegree (C a * X ^ (n + 1)) = 0 ∨ M (C a * X ^ (n + 1))

Next tactic:
refine' Or.inr _
/-- A property holds for all polynomials of non-zero `natDegree` with coefficients in a
semiring `R` if it holds for
* `p + a`, with `a ∈ R`, `p ∈ R[X]`,
* `p + q`, with `p, q ∈ R[X]`,
* monomials with nonzero coefficient and non-zero exponent,
with appropriate restrictions on each term.
Note that multiplication is "hidden" in the assumption on monomials, so there is no explicit
multiplication in the statement.
See `degree_pos_induction_on` for a similar statement involving more explicit multiplications.
 -/
@[elab_as_elim]
theorem natDegree_ne_zero_induction_on {M : R[X] → Prop} {f : R[X]} (f0 : f.natDegree ≠ 0)
    (h_C_add : ∀ {a p}, M p → M (C a + p)) (h_add : ∀ {p q}, M p → M q → M (p + q))
    (h_monomial : ∀ {n : ℕ} {a : R}, a ≠ 0 → n ≠ 0 → M (monomial n a)) : M f := by
  suffices f.natDegree = 0 ∨ M f from Or.recOn this (fun h => (f0 h).elim) id
  refine Polynomial.induction_on f ?_ ?_ ?_
  · exact fun a => Or.inl (natDegree_C _)
  · rintro p q (hp | hp) (hq | hq)
    · refine' Or.inl _
      rw [eq_C_of_natDegree_eq_zero hp, eq_C_of_natDegree_eq_zero hq, ← C_add, natDegree_C]
    · refine' Or.inr _
      rw [eq_C_of_natDegree_eq_zero hp]
      exact h_C_add hq
    · refine' Or.inr _
      rw [eq_C_of_natDegree_eq_zero hq, add_comm]
      exact h_C_add hp
    · exact Or.inr (h_add hp hq)
  · intro n a _
    by_cases a0 : a = 0
    · exact Or.inl (by rw [a0, C_0, zero_mul, natDegree_zero])
    · refine' Or.inr _
      

Proof state:
case neg
R : Type u
S : Type v
T : Type w
A : Type z
a✝¹ b : R
n✝ : ℕ
inst✝ : Semiring R
p q : R[X]
M : R[X] → Prop
f : R[X]
f0 : natDegree f ≠ 0
h_C_add : ∀ {a : R} {p : R[X]}, M p → M (C a + p)
h_add : ∀ {p q : R[X]}, M p → M q → M (p + q)
h_monomial : ∀ {n : ℕ} {a : R}, a ≠ 0 → n ≠ 0 → M ((monomial n) a)
n : ℕ
a : R
a✝ : natDegree (C a * X ^ n) = 0 ∨ M (C a * X ^ n)
a0 : ¬a = 0
⊢ M (C a * X ^ (n + 1))

Next tactic:
rw [C_mul_X_pow_eq_monomial]
/-- A property holds for all polynomials of non-zero `natDegree` with coefficients in a
semiring `R` if it holds for
* `p + a`, with `a ∈ R`, `p ∈ R[X]`,
* `p + q`, with `p, q ∈ R[X]`,
* monomials with nonzero coefficient and non-zero exponent,
with appropriate restrictions on each term.
Note that multiplication is "hidden" in the assumption on monomials, so there is no explicit
multiplication in the statement.
See `degree_pos_induction_on` for a similar statement involving more explicit multiplications.
 -/
@[elab_as_elim]
theorem natDegree_ne_zero_induction_on {M : R[X] → Prop} {f : R[X]} (f0 : f.natDegree ≠ 0)
    (h_C_add : ∀ {a p}, M p → M (C a + p)) (h_add : ∀ {p q}, M p → M q → M (p + q))
    (h_monomial : ∀ {n : ℕ} {a : R}, a ≠ 0 → n ≠ 0 → M (monomial n a)) : M f := by
  suffices f.natDegree = 0 ∨ M f from Or.recOn this (fun h => (f0 h).elim) id
  refine Polynomial.induction_on f ?_ ?_ ?_
  · exact fun a => Or.inl (natDegree_C _)
  · rintro p q (hp | hp) (hq | hq)
    · refine' Or.inl _
      rw [eq_C_of_natDegree_eq_zero hp, eq_C_of_natDegree_eq_zero hq, ← C_add, natDegree_C]
    · refine' Or.inr _
      rw [eq_C_of_natDegree_eq_zero hp]
      exact h_C_add hq
    · refine' Or.inr _
      rw [eq_C_of_natDegree_eq_zero hq, add_comm]
      exact h_C_add hp
    · exact Or.inr (h_add hp hq)
  · intro n a _
    by_cases a0 : a = 0
    · exact Or.inl (by rw [a0, C_0, zero_mul, natDegree_zero])
    · refine' Or.inr _
      rw [C_mul_X_pow_eq_monomial]
      

Proof state:
case neg
R : Type u
S : Type v
T : Type w
A : Type z
a✝¹ b : R
n✝ : ℕ
inst✝ : Semiring R
p q : R[X]
M : R[X] → Prop
f : R[X]
f0 : natDegree f ≠ 0
h_C_add : ∀ {a : R} {p : R[X]}, M p → M (C a + p)
h_add : ∀ {p q : R[X]}, M p → M q → M (p + q)
h_monomial : ∀ {n : ℕ} {a : R}, a ≠ 0 → n ≠ 0 → M ((monomial n) a)
n : ℕ
a : R
a✝ : natDegree (C a * X ^ n) = 0 ∨ M (C a * X ^ n)
a0 : ¬a = 0
⊢ M ((monomial (n + 1)) a)

Next tactic:
exact h_monomial a0 n.succ_ne_zero
/-- **Hahn decomposition theorem** -/
theorem hahn_decomposition [IsFiniteMeasure μ] [IsFiniteMeasure ν] :
    ∃ s,
      MeasurableSet s ∧
        (∀ t, MeasurableSet t → t ⊆ s → ν t ≤ μ t) ∧ ∀ t, MeasurableSet t → t ⊆ sᶜ → μ t ≤ ν t := by
  

Proof state:
α : Type u_1
inst✝² : MeasurableSpace α
μ ν : Measure α
inst✝¹ : IsFiniteMeasure μ
inst✝ : IsFiniteMeasure ν
⊢ ∃ s,
    MeasurableSet s ∧
      (∀ (t : Set α), MeasurableSet t → t ⊆ s → ↑↑ν t ≤ ↑↑μ t) ∧ ∀ (t : Set α), MeasurableSet t → t ⊆ sᶜ → ↑↑μ t ≤ ↑↑ν t

Next tactic:
let d : Set α → ℝ := fun s => ((μ s).toNNReal : ℝ) - (ν s).toNNReal
/-- **Hahn decomposition theorem** -/
theorem hahn_decomposition [IsFiniteMeasure μ] [IsFiniteMeasure ν] :
    ∃ s,
      MeasurableSet s ∧
        (∀ t, MeasurableSet t → t ⊆ s → ν t ≤ μ t) ∧ ∀ t, MeasurableSet t → t ⊆ sᶜ → μ t ≤ ν t := by
  let d : Set α → ℝ := fun s => ((μ s).toNNReal : ℝ) - (ν s).toNNReal
  

Proof state:
α : Type u_1
inst✝² : MeasurableSpace α
μ ν : Measure α
inst✝¹ : IsFiniteMeasure μ
inst✝ : IsFiniteMeasure ν
d : Set α → ℝ := fun s => ↑(ENNReal.toNNReal (↑↑μ s)) - ↑(ENNReal.toNNReal (↑↑ν s))
⊢ ∃ s,
    MeasurableSet s ∧
      (∀ (t : Set α), MeasurableSet t → t ⊆ s → ↑↑ν t ≤ ↑↑μ t) ∧ ∀ (t : Set α), MeasurableSet t → t ⊆ sᶜ → ↑↑μ t ≤ ↑↑ν t

Next tactic:
let c : Set ℝ := d '' { s | MeasurableSet s }
/-- **Hahn decomposition theorem** -/
theorem hahn_decomposition [IsFiniteMeasure μ] [IsFiniteMeasure ν] :
    ∃ s,
      MeasurableSet s ∧
        (∀ t, MeasurableSet t → t ⊆ s → ν t ≤ μ t) ∧ ∀ t, MeasurableSet t → t ⊆ sᶜ → μ t ≤ ν t := by
  let d : Set α → ℝ := fun s => ((μ s).toNNReal : ℝ) - (ν s).toNNReal
  let c : Set ℝ := d '' { s | MeasurableSet s }
  

Proof state:
α : Type u_1
inst✝² : MeasurableSpace α
μ ν : Measure α
inst✝¹ : IsFiniteMeasure μ
inst✝ : IsFiniteMeasure ν
d : Set α → ℝ := fun s => ↑(ENNReal.toNNReal (↑↑μ s)) - ↑(ENNReal.toNNReal (↑↑ν s))
c : Set ℝ := d '' {s | MeasurableSet s}
⊢ ∃ s,
    MeasurableSet s ∧
      (∀ (t : Set α), MeasurableSet t → t ⊆ s → ↑↑ν t ≤ ↑↑μ t) ∧ ∀ (t : Set α), MeasurableSet t → t ⊆ sᶜ → ↑↑μ t ≤ ↑↑ν t

Next tactic:
let γ : ℝ := sSup c
/-- **Hahn decomposition theorem** -/
theorem hahn_decomposition [IsFiniteMeasure μ] [IsFiniteMeasure ν] :
    ∃ s,
      MeasurableSet s ∧
        (∀ t, MeasurableSet t → t ⊆ s → ν t ≤ μ t) ∧ ∀ t, MeasurableSet t → t ⊆ sᶜ → μ t ≤ ν t := by
  let d : Set α → ℝ := fun s => ((μ s).toNNReal : ℝ) - (ν s).toNNReal
  let c : Set ℝ := d '' { s | MeasurableSet s }
  let γ : ℝ := sSup c
  

Proof state:
α : Type u_1
inst✝² : MeasurableSpace α
μ ν : Measure α
inst✝¹ : IsFiniteMeasure μ
inst✝ : IsFiniteMeasure ν
d : Set α → ℝ := fun s => ↑(ENNReal.toNNReal (↑↑μ s)) - ↑(ENNReal.toNNReal (↑↑ν s))
c : Set ℝ := d '' {s | MeasurableSet s}
γ : ℝ := sSup c
⊢ ∃ s,
    MeasurableSet s ∧
      (∀ (t : Set α), MeasurableSet t → t ⊆ s → ↑↑ν t ≤ ↑↑μ t) ∧ ∀ (t : Set α), MeasurableSet t → t ⊆ sᶜ → ↑↑μ t ≤ ↑↑ν t

Next tactic:
have hμ : ∀ s, μ s ≠ ∞ := measure_ne_top μ
/-- **Hahn decomposition theorem** -/
theorem hahn_decomposition [IsFiniteMeasure μ] [IsFiniteMeasure ν] :
    ∃ s,
      MeasurableSet s ∧
        (∀ t, MeasurableSet t → t ⊆ s → ν t ≤ μ t) ∧ ∀ t, MeasurableSet t → t ⊆ sᶜ → μ t ≤ ν t := by
  let d : Set α → ℝ := fun s => ((μ s).toNNReal : ℝ) - (ν s).toNNReal
  let c : Set ℝ := d '' { s | MeasurableSet s }
  let γ : ℝ := sSup c
  have hμ : ∀ s, μ s ≠ ∞ := measure_ne_top μ
  

Proof state:
α : Type u_1
inst✝² : MeasurableSpace α
μ ν : Measure α
inst✝¹ : IsFiniteMeasure μ
inst✝ : IsFiniteMeasure ν
d : Set α → ℝ := fun s => ↑(ENNReal.toNNReal (↑↑μ s)) - ↑(ENNReal.toNNReal (↑↑ν s))
c : Set ℝ := d '' {s | MeasurableSet s}
γ : ℝ := sSup c
hμ : ∀ (s : Set α), ↑↑μ s ≠ ⊤
⊢ ∃ s,
    MeasurableSet s ∧
      (∀ (t : Set α), MeasurableSet t → t ⊆ s → ↑↑ν t ≤ ↑↑μ t) ∧ ∀ (t : Set α), MeasurableSet t → t ⊆ sᶜ → ↑↑μ t ≤ ↑↑ν t

Next tactic:
have hν : ∀ s, ν s ≠ ∞ := measure_ne_top ν
/-- **Hahn decomposition theorem** -/
theorem hahn_decomposition [IsFiniteMeasure μ] [IsFiniteMeasure ν] :
    ∃ s,
      MeasurableSet s ∧
        (∀ t, MeasurableSet t → t ⊆ s → ν t ≤ μ t) ∧ ∀ t, MeasurableSet t → t ⊆ sᶜ → μ t ≤ ν t := by
  let d : Set α → ℝ := fun s => ((μ s).toNNReal : ℝ) - (ν s).toNNReal
  let c : Set ℝ := d '' { s | MeasurableSet s }
  let γ : ℝ := sSup c
  have hμ : ∀ s, μ s ≠ ∞ := measure_ne_top μ
  have hν : ∀ s, ν s ≠ ∞ := measure_ne_top ν
  

Proof state:
α : Type u_1
inst✝² : MeasurableSpace α
μ ν : Measure α
inst✝¹ : IsFiniteMeasure μ
inst✝ : IsFiniteMeasure ν
d : Set α → ℝ := fun s => ↑(ENNReal.toNNReal (↑↑μ s)) - ↑(ENNReal.toNNReal (↑↑ν s))
c : Set ℝ := d '' {s | MeasurableSet s}
γ : ℝ := sSup c
hμ : ∀ (s : Set α), ↑↑μ s ≠ ⊤
hν : ∀ (s : Set α), ↑↑ν s ≠ ⊤
⊢ ∃ s,
    MeasurableSet s ∧
      (∀ (t : Set α), MeasurableSet t → t ⊆ s → ↑↑ν t ≤ ↑↑μ t) ∧ ∀ (t : Set α), MeasurableSet t → t ⊆ sᶜ → ↑↑μ t ≤ ↑↑ν t

Next tactic:
have to_nnreal_μ : ∀ s, ((μ s).toNNReal : ℝ≥0∞) = μ s := fun s => ENNReal.coe_toNNReal <| hμ _
/-- **Hahn decomposition theorem** -/
theorem hahn_decomposition [IsFiniteMeasure μ] [IsFiniteMeasure ν] :
    ∃ s,
      MeasurableSet s ∧
        (∀ t, MeasurableSet t → t ⊆ s → ν t ≤ μ t) ∧ ∀ t, MeasurableSet t → t ⊆ sᶜ → μ t ≤ ν t := by
  let d : Set α → ℝ := fun s => ((μ s).toNNReal : ℝ) - (ν s).toNNReal
  let c : Set ℝ := d '' { s | MeasurableSet s }
  let γ : ℝ := sSup c
  have hμ : ∀ s, μ s ≠ ∞ := measure_ne_top μ
  have hν : ∀ s, ν s ≠ ∞ := measure_ne_top ν
  have to_nnreal_μ : ∀ s, ((μ s).toNNReal : ℝ≥0∞) = μ s := fun s => ENNReal.coe_toNNReal <| hμ _
  

Proof state:
α : Type u_1
inst✝² : MeasurableSpace α
μ ν : Measure α
inst✝¹ : IsFiniteMeasure μ
inst✝ : IsFiniteMeasure ν
d : Set α → ℝ := fun s => ↑(ENNReal.toNNReal (↑↑μ s)) - ↑(ENNReal.toNNReal (↑↑ν s))
c : Set ℝ := d '' {s | MeasurableSet s}
γ : ℝ := sSup c
hμ : ∀ (s : Set α), ↑↑μ s ≠ ⊤
hν : ∀ (s : Set α), ↑↑ν s ≠ ⊤
to_nnreal_μ : ∀ (s : Set α), ↑(ENNReal.toNNReal (↑↑μ s)) = ↑↑μ s
⊢ ∃ s,
    MeasurableSet s ∧
      (∀ (t : Set α), MeasurableSet t → t ⊆ s → ↑↑ν t ≤ ↑↑μ t) ∧ ∀ (t : Set α), MeasurableSet t → t ⊆ sᶜ → ↑↑μ t ≤ ↑↑ν t

Next tactic:
have to_nnreal_ν : ∀ s, ((ν s).toNNReal : ℝ≥0∞) = ν s := fun s => ENNReal.coe_toNNReal <| hν _
/-- **Hahn decomposition theorem** -/
theorem hahn_decomposition [IsFiniteMeasure μ] [IsFiniteMeasure ν] :
    ∃ s,
      MeasurableSet s ∧
        (∀ t, MeasurableSet t → t ⊆ s → ν t ≤ μ t) ∧ ∀ t, MeasurableSet t → t ⊆ sᶜ → μ t ≤ ν t := by
  let d : Set α → ℝ := fun s => ((μ s).toNNReal : ℝ) - (ν s).toNNReal
  let c : Set ℝ := d '' { s | MeasurableSet s }
  let γ : ℝ := sSup c
  have hμ : ∀ s, μ s ≠ ∞ := measure_ne_top μ
  have hν : ∀ s, ν s ≠ ∞ := measure_ne_top ν
  have to_nnreal_μ : ∀ s, ((μ s).toNNReal : ℝ≥0∞) = μ s := fun s => ENNReal.coe_toNNReal <| hμ _
  have to_nnreal_ν : ∀ s, ((ν s).toNNReal : ℝ≥0∞) = ν s := fun s => ENNReal.coe_toNNReal <| hν _
  

Proof state:
α : Type u_1
inst✝² : MeasurableSpace α
μ ν : Measure α
inst✝¹ : IsFiniteMeasure μ
inst✝ : IsFiniteMeasure ν
d : Set α → ℝ := fun s => ↑(ENNReal.toNNReal (↑↑μ s)) - ↑(ENNReal.toNNReal (↑↑ν s))
c : Set ℝ := d '' {s | MeasurableSet s}
γ : ℝ := sSup c
hμ : ∀ (s : Set α), ↑↑μ s ≠ ⊤
hν : ∀ (s : Set α), ↑↑ν s ≠ ⊤
to_nnreal_μ : ∀ (s : Set α), ↑(ENNReal.toNNReal (↑↑μ s)) = ↑↑μ s
to_nnreal_ν : ∀ (s : Set α), ↑(ENNReal.toNNReal (↑↑ν s)) = ↑↑ν s
⊢ ∃ s,
    MeasurableSet s ∧
      (∀ (t : Set α), MeasurableSet t → t ⊆ s → ↑↑ν t ≤ ↑↑μ t) ∧ ∀ (t : Set α), MeasurableSet t → t ⊆ sᶜ → ↑↑μ t ≤ ↑↑ν t

Next tactic:
have d_split : ∀ s t, MeasurableSet s → MeasurableSet t → d s = d (s \ t) + d (s ∩ t) := by
    intro s t _hs ht
    dsimp only
    rw [← measure_inter_add_diff s ht, ← measure_inter_add_diff s ht,
      ENNReal.toNNReal_add (hμ _) (hμ _), ENNReal.toNNReal_add (hν _) (hν _), NNReal.coe_add,
      NNReal.coe_add]
    simp only [sub_eq_add_neg, neg_add]
    abel
/-- **Hahn decomposition theorem** -/
theorem hahn_decomposition [IsFiniteMeasure μ] [IsFiniteMeasure ν] :
    ∃ s,
      MeasurableSet s ∧
        (∀ t, MeasurableSet t → t ⊆ s → ν t ≤ μ t) ∧ ∀ t, MeasurableSet t → t ⊆ sᶜ → μ t ≤ ν t := by
  let d : Set α → ℝ := fun s => ((μ s).toNNReal : ℝ) - (ν s).toNNReal
  let c : Set ℝ := d '' { s | MeasurableSet s }
  let γ : ℝ := sSup c
  have hμ : ∀ s, μ s ≠ ∞ := measure_ne_top μ
  have hν : ∀ s, ν s ≠ ∞ := measure_ne_top ν
  have to_nnreal_μ : ∀ s, ((μ s).toNNReal : ℝ≥0∞) = μ s := fun s => ENNReal.coe_toNNReal <| hμ _
  have to_nnreal_ν : ∀ s, ((ν s).toNNReal : ℝ≥0∞) = ν s := fun s => ENNReal.coe_toNNReal <| hν _
  have d_split : ∀ s t, MeasurableSet s → MeasurableSet t → d s = d (s \ t) + d (s ∩ t) := by
    

Proof state:
α : Type u_1
inst✝² : MeasurableSpace α
μ ν : Measure α
inst✝¹ : IsFiniteMeasure μ
inst✝ : IsFiniteMeasure ν
d : Set α → ℝ := fun s => ↑(ENNReal.toNNReal (↑↑μ s)) - ↑(ENNReal.toNNReal (↑↑ν s))
c : Set ℝ := d '' {s | MeasurableSet s}
γ : ℝ := sSup c
hμ : ∀ (s : Set α), ↑↑μ s ≠ ⊤
hν : ∀ (s : Set α), ↑↑ν s ≠ ⊤
to_nnreal_μ : ∀ (s : Set α), ↑(ENNReal.toNNReal (↑↑μ s)) = ↑↑μ s
to_nnreal_ν : ∀ (s : Set α), ↑(ENNReal.toNNReal (↑↑ν s)) = ↑↑ν s
⊢ ∀ (s t : Set α), MeasurableSet s → MeasurableSet t → d s = d (s \ t) + d (s ∩ t)

Next tactic:
intro s t _hs ht
/-- **Hahn decomposition theorem** -/
theorem hahn_decomposition [IsFiniteMeasure μ] [IsFiniteMeasure ν] :
    ∃ s,
      MeasurableSet s ∧
        (∀ t, MeasurableSet t → t ⊆ s → ν t ≤ μ t) ∧ ∀ t, MeasurableSet t → t ⊆ sᶜ → μ t ≤ ν t := by
  let d : Set α → ℝ := fun s => ((μ s).toNNReal : ℝ) - (ν s).toNNReal
  let c : Set ℝ := d '' { s | MeasurableSet s }
  let γ : ℝ := sSup c
  have hμ : ∀ s, μ s ≠ ∞ := measure_ne_top μ
  have hν : ∀ s, ν s ≠ ∞ := measure_ne_top ν
  have to_nnreal_μ : ∀ s, ((μ s).toNNReal : ℝ≥0∞) = μ s := fun s => ENNReal.coe_toNNReal <| hμ _
  have to_nnreal_ν : ∀ s, ((ν s).toNNReal : ℝ≥0∞) = ν s := fun s => ENNReal.coe_toNNReal <| hν _
  have d_split : ∀ s t, MeasurableSet s → MeasurableSet t → d s = d (s \ t) + d (s ∩ t) := by
    intro s t _hs ht
    

Proof state:
α : Type u_1
inst✝² : MeasurableSpace α
μ ν : Measure α
inst✝¹ : IsFiniteMeasure μ
inst✝ : IsFiniteMeasure ν
d : Set α → ℝ := fun s => ↑(ENNReal.toNNReal (↑↑μ s)) - ↑(ENNReal.toNNReal (↑↑ν s))
c : Set ℝ := d '' {s | MeasurableSet s}
γ : ℝ := sSup c
hμ : ∀ (s : Set α), ↑↑μ s ≠ ⊤
hν : ∀ (s : Set α), ↑↑ν s ≠ ⊤
to_nnreal_μ : ∀ (s : Set α), ↑(ENNReal.toNNReal (↑↑μ s)) = ↑↑μ s
to_nnreal_ν : ∀ (s : Set α), ↑(ENNReal.toNNReal (↑↑ν s)) = ↑↑ν s
s t : Set α
_hs : MeasurableSet s
ht : MeasurableSet t
⊢ d s = d (s \ t) + d (s ∩ t)

Next tactic:
dsimp only
/-- **Hahn decomposition theorem** -/
theorem hahn_decomposition [IsFiniteMeasure μ] [IsFiniteMeasure ν] :
    ∃ s,
      MeasurableSet s ∧
        (∀ t, MeasurableSet t → t ⊆ s → ν t ≤ μ t) ∧ ∀ t, MeasurableSet t → t ⊆ sᶜ → μ t ≤ ν t := by
  let d : Set α → ℝ := fun s => ((μ s).toNNReal : ℝ) - (ν s).toNNReal
  let c : Set ℝ := d '' { s | MeasurableSet s }
  let γ : ℝ := sSup c
  have hμ : ∀ s, μ s ≠ ∞ := measure_ne_top μ
  have hν : ∀ s, ν s ≠ ∞ := measure_ne_top ν
  have to_nnreal_μ : ∀ s, ((μ s).toNNReal : ℝ≥0∞) = μ s := fun s => ENNReal.coe_toNNReal <| hμ _
  have to_nnreal_ν : ∀ s, ((ν s).toNNReal : ℝ≥0∞) = ν s := fun s => ENNReal.coe_toNNReal <| hν _
  have d_split : ∀ s t, MeasurableSet s → MeasurableSet t → d s = d (s \ t) + d (s ∩ t) := by
    intro s t _hs ht
    dsimp only
    

Proof state:
α : Type u_1
inst✝² : MeasurableSpace α
μ ν : Measure α
inst✝¹ : IsFiniteMeasure μ
inst✝ : IsFiniteMeasure ν
d : Set α → ℝ := fun s => ↑(ENNReal.toNNReal (↑↑μ s)) - ↑(ENNReal.toNNReal (↑↑ν s))
c : Set ℝ := d '' {s | MeasurableSet s}
γ : ℝ := sSup c
hμ : ∀ (s : Set α), ↑↑μ s ≠ ⊤
hν : ∀ (s : Set α), ↑↑ν s ≠ ⊤
to_nnreal_μ : ∀ (s : Set α), ↑(ENNReal.toNNReal (↑↑μ s)) = ↑↑μ s
to_nnreal_ν : ∀ (s : Set α), ↑(ENNReal.toNNReal (↑↑ν s)) = ↑↑ν s
s t : Set α
_hs : MeasurableSet s
ht : MeasurableSet t
⊢ ↑(ENNReal.toNNReal (↑↑μ s)) - ↑(ENNReal.toNNReal (↑↑ν s)) =
    ↑(ENNReal.toNNReal (↑↑μ (s \ t))) - ↑(ENNReal.toNNReal (↑↑ν (s \ t))) +
      (↑(ENNReal.toNNReal (↑↑μ (s ∩ t))) - ↑(ENNReal.toNNReal (↑↑ν (s ∩ t))))

Next tactic:
rw [← measure_inter_add_diff s ht, ← measure_inter_add_diff s ht,
      ENNReal.toNNReal_add (hμ _) (hμ _), ENNReal.toNNReal_add (hν _) (hν _), NNReal.coe_add,
      NNReal.coe_add]