-- Mathlib/Combinatorics/SetFamily/AhlswedeZhang.lean
private lemma Fintype.sum_div_mul_card_choose_card :
    ∑ s : Finset α, (card α / ((card α - #s) * (card α).choose #s) : ℚ) =
      card α * ∑ k ∈ range (card α), (↑k)⁻¹ + 1

Proof state:
α : Type u_1
inst✝¹ : Fintype α
inst✝ : Nonempty α
this :
  ∀ {x : ℕ},
    ∀ s ∈ powersetCard x univ,
      ↑(card α) / ((↑(card α) - ↑(#s)) * ↑((card α).choose #s)) = ↑(card α) / ((↑(card α) - ↑x) * ↑((card α).choose x))
⊢ ↑(card α) * ∑ i ∈ range (card α + 1), ↑((card α).choose i) / ((↑(card α) - ↑i) * ↑((card α).choose i)) =
    ↑(card α) * ∑ x ∈ range (card α).succ, (↑x)⁻¹

Tactic:
have (n) (hn : n ∈ range (card α + 1)) :
    ((card α).choose n / ((card α - n) * (card α).choose n) : ℚ) = (card α - n : ℚ)⁻¹ := by
  rw [div_mul_cancel_right₀]
  exact cast_ne_zero.2 (choose_pos <| mem_range_succ_iff.1 hn).ne'

Result:
α : Type u_1
inst✝¹ : Fintype α
inst✝ : Nonempty α
this✝ :
  ∀ {x : ℕ},
    ∀ s ∈ powersetCard x univ,
      ↑(card α) / ((↑(card α) - ↑(#s)) * ↑((card α).choose #s)) = ↑(card α) / ((↑(card α) - ↑x) * ↑((card α).choose x))
this : ∀ n ∈ range (card α + 1), ↑((card α).choose n) / ((↑(card α) - ↑n) * ↑((card α).choose n)) = (↑(card α) - ↑n)⁻¹
⊢ ↑(card α) * ∑ i ∈ range (card α + 1), ↑((card α).choose i) / ((↑(card α) - ↑i) * ↑((card α).choose i)) =
    ↑(card α) * ∑ x ∈ range (card α).succ, (↑x)⁻¹

Proof state:
α : Type u_1
inst✝¹ : Fintype α
inst✝ : Nonempty α
⊢ ∀ {x : ℕ},
    ∀ s ∈ powersetCard x univ,
      ↑(card α) / ((↑(card α) - ↑(#s)) * ↑((card α).choose #s)) = ↑(card α) / ((↑(card α) - ↑x) * ↑((card α).choose x))

Tactic:
intros n s hs

Result:
α : Type u_1
inst✝¹ : Fintype α
inst✝ : Nonempty α
n : ℕ
s : Finset α
hs : s ∈ powersetCard n univ
⊢ ↑(card α) / ((↑(card α) - ↑(#s)) * ↑((card α).choose #s)) = ↑(card α) / ((↑(card α) - ↑n) * ↑((card α).choose n))

Proof state:
case hb
α : Type u_1
inst✝¹ : Fintype α
inst✝ : Nonempty α
this :
  ∀ {x : ℕ},
    ∀ s ∈ powersetCard x univ,
      ↑(card α) / ((↑(card α) - ↑(#s)) * ↑((card α).choose #s)) = ↑(card α) / ((↑(card α) - ↑x) * ↑((card α).choose x))
n : ℕ
hn : n ∈ range (card α + 1)
⊢ ↑((card α).choose n) ≠ 0

Tactic:
exact cast_ne_zero.2 (choose_pos <| mem_range_succ_iff.1 hn).ne'

Result:
no goals

Proof state:
α : Type u_1
inst✝¹ : Fintype α
inst✝ : Nonempty α
this :
  ∀ {x : ℕ},
    ∀ s ∈ powersetCard x univ,
      ↑(card α) / ((↑(card α) - ↑(#s)) * ↑((card α).choose #s)) = ↑(card α) / ((↑(card α) - ↑x) * ↑((card α).choose x))
n : ℕ
hn : n ∈ range (card α + 1)
⊢ ↑((card α).choose n) / ((↑(card α) - ↑n) * ↑((card α).choose n)) = (↑(card α) - ↑n)⁻¹

Tactic:
rw [div_mul_cancel_right₀]

Result:
case hb
α : Type u_1
inst✝¹ : Fintype α
inst✝ : Nonempty α
this :
  ∀ {x : ℕ},
    ∀ s ∈ powersetCard x univ,
      ↑(card α) / ((↑(card α) - ↑(#s)) * ↑((card α).choose #s)) = ↑(card α) / ((↑(card α) - ↑x) * ↑((card α).choose x))
n : ℕ
hn : n ∈ range (card α + 1)
⊢ ↑((card α).choose n) ≠ 0

Proof state:
α : Type u_1
inst✝¹ : Fintype α
inst✝ : Nonempty α
n : ℕ
s : Finset α
hs : s ∈ powersetCard n univ
⊢ ↑(card α) / ((↑(card α) - ↑(#s)) * ↑((card α).choose #s)) = ↑(card α) / ((↑(card α) - ↑n) * ↑((card α).choose n))

Tactic:
rw [mem_powersetCard_univ.1 hs]

Result:
no goals

Proof state:
case h.e'_1.h.e'_2.a
α : Type u_1
inst✝¹ : Fintype α
inst✝ : Nonempty α
this✝ :
  ∀ {x : ℕ},
    ∀ s ∈ powersetCard x univ,
      ↑(card α) / ((↑(card α) - ↑(#s)) * ↑((card α).choose #s)) = ↑(card α) / ((↑(card α) - ↑x) * ↑((card α).choose x))
this : ∀ n ∈ range (card α + 1), ↑((card α).choose n) / ((↑(card α) - ↑n) * ↑((card α).choose n)) = (↑(card α) - ↑n)⁻¹
a : ℕ
ha : a ∈ range (card α + 1)
⊢ (↑(card α) - ↑a)⁻¹ = (↑(card α + 1 - 1 - a))⁻¹

Tactic:
rw [add_tsub_cancel_right, cast_sub (mem_range_succ_iff.mp ha)]

Result:
no goals

Proof state:
α : Type u_1
inst✝¹ : Fintype α
inst✝ : Nonempty α
this :
  ∀ {x : ℕ},
    ∀ s ∈ powersetCard x univ,
      ↑(card α) / ((↑(card α) - ↑(#s)) * ↑((card α).choose #s)) = ↑(card α) / ((↑(card α) - ↑x) * ↑((card α).choose x))
⊢ ∑ x ∈ range (card α + 1), ↑(card α) * (↑((card α).choose x) / ((↑(card α) - ↑x) * ↑((card α).choose x))) =
    ↑(card α) * ∑ k ∈ range (card α), (↑k)⁻¹ + 1

Tactic:
rw [← mul_sum, ← mul_inv_cancel₀ (cast_ne_zero.mpr card_ne_zero : (card α : ℚ) ≠ 0), ← mul_add,
  add_comm _ ((card α)⁻¹ : ℚ), ← sum_insert (f := fun x : ℕ ↦ (x⁻¹ : ℚ)) not_mem_range_self,
  ← range_succ]

Result:
α : Type u_1
inst✝¹ : Fintype α
inst✝ : Nonempty α
this :
  ∀ {x : ℕ},
    ∀ s ∈ powersetCard x univ,
      ↑(card α) / ((↑(card α) - ↑(#s)) * ↑((card α).choose #s)) = ↑(card α) / ((↑(card α) - ↑x) * ↑((card α).choose x))
⊢ ↑(card α) * ∑ i ∈ range (card α + 1), ↑((card α).choose i) / ((↑(card α) - ↑i) * ↑((card α).choose i)) =
    ↑(card α) * ∑ x ∈ range (card α).succ, (↑x)⁻¹

Proof state:
α : Type u_1
inst✝¹ : Fintype α
inst✝ : Nonempty α
this✝ :
  ∀ {x : ℕ},
    ∀ s ∈ powersetCard x univ,
      ↑(card α) / ((↑(card α) - ↑(#s)) * ↑((card α).choose #s)) = ↑(card α) / ((↑(card α) - ↑x) * ↑((card α).choose x))
this : ∀ n ∈ range (card α + 1), ↑((card α).choose n) / ((↑(card α) - ↑n) * ↑((card α).choose n)) = (↑(card α) - ↑n)⁻¹
⊢ ↑(card α) * ∑ i ∈ range (card α + 1), ↑((card α).choose i) / ((↑(card α) - ↑i) * ↑((card α).choose i)) =
    ↑(card α) * ∑ x ∈ range (card α).succ, (↑x)⁻¹

Tactic:
simp only [sum_congr rfl this, mul_eq_mul_left_iff, cast_eq_zero]

Result:
α : Type u_1
inst✝¹ : Fintype α
inst✝ : Nonempty α
this✝ :
  ∀ {x : ℕ},
    ∀ s ∈ powersetCard x univ,
      ↑(card α) / ((↑(card α) - ↑(#s)) * ↑((card α).choose #s)) = ↑(card α) / ((↑(card α) - ↑x) * ↑((card α).choose x))
this : ∀ n ∈ range (card α + 1), ↑((card α).choose n) / ((↑(card α) - ↑n) * ↑((card α).choose n)) = (↑(card α) - ↑n)⁻¹
⊢ ∑ x ∈ range (card α + 1), (↑(card α) - ↑x)⁻¹ = ∑ x ∈ range (card α).succ, (↑x)⁻¹ ∨ card α = 0

Proof state:
α : Type u_1
inst✝¹ : Fintype α
inst✝ : Nonempty α
this✝ :
  ∀ {x : ℕ},
    ∀ s ∈ powersetCard x univ,
      ↑(card α) / ((↑(card α) - ↑(#s)) * ↑((card α).choose #s)) = ↑(card α) / ((↑(card α) - ↑x) * ↑((card α).choose x))
this : ∀ n ∈ range (card α + 1), ↑((card α).choose n) / ((↑(card α) - ↑n) * ↑((card α).choose n)) = (↑(card α) - ↑n)⁻¹
⊢ ∑ x ∈ range (card α + 1), (↑(card α) - ↑x)⁻¹ = ∑ x ∈ range (card α).succ, (↑x)⁻¹ ∨ card α = 0

Tactic:
convert Or.inl <| sum_range_reflect _ _ with a ha

Result:
case h.e'_1.h.e'_2.a
α : Type u_1
inst✝¹ : Fintype α
inst✝ : Nonempty α
this✝ :
  ∀ {x : ℕ},
    ∀ s ∈ powersetCard x univ,
      ↑(card α) / ((↑(card α) - ↑(#s)) * ↑((card α).choose #s)) = ↑(card α) / ((↑(card α) - ↑x) * ↑((card α).choose x))
this : ∀ n ∈ range (card α + 1), ↑((card α).choose n) / ((↑(card α) - ↑n) * ↑((card α).choose n)) = (↑(card α) - ↑n)⁻¹
a : ℕ
ha : a ∈ range (card α + 1)
⊢ (↑(card α) - ↑a)⁻¹ = (↑(card α + 1 - 1 - a))⁻¹

Proof state:
α : Type u_1
inst✝¹ : Fintype α
inst✝ : Nonempty α
⊢ ∑ s : Finset α, ↑(card α) / ((↑(card α) - ↑(#s)) * ↑((card α).choose #s)) =
    ↑(card α) * ∑ k ∈ range (card α), (↑k)⁻¹ + 1

Tactic:
rw [← powerset_univ, powerset_card_disjiUnion, sum_disjiUnion]

Result:
α : Type u_1
inst✝¹ : Fintype α
inst✝ : Nonempty α
⊢ ∑ i ∈ range (#univ + 1), ∑ x ∈ powersetCard i univ, ↑(card α) / ((↑(card α) - ↑(#x)) * ↑((card α).choose #x)) =
    ↑(card α) * ∑ k ∈ range (card α), (↑k)⁻¹ + 1