symm
case a.mp.intro.intro.intro
α : Type u_1
inst✝ : LinearOrder α
s U V : Finset α
n r k i : ℕ
𝒜 𝒞✝ : Finset (Finset (Fin n))
hir : i ≤ r
hrk : r ≤ k
hkn : k ≤ n
h₁ : Set.Sized r ↑𝒜
h₂ : k.choose r ≤ 𝒜.card
range'k : Finset (Fin n) := (range k).attachFin ⋯
𝒞 : Finset (Finset (Fin n)) := powersetCard r range'k
Ccard : 𝒞.card = k.choose r
this : Set.Sized r ↑𝒞
B A : Finset (Fin n)
Ah : A ⊆ range'k ∧ A.card = r
BsubA : B ⊆ A
card_sdiff_i : (A \ B).card = i
⊢ B.card = r - i
case a.mp.intro.intro.intro
α : Type u_1
inst✝ : LinearOrder α
s U V : Finset α
n r k i : ℕ
𝒜 𝒞✝ : Finset (Finset (Fin n))
hir : i ≤ r
hrk : r ≤ k
hkn : k ≤ n
h₁ : Set.Sized r ↑𝒜
h₂ : k.choose r ≤ 𝒜.card
range'k : Finset (Fin n) := (range k).attachFin ⋯
𝒞 : Finset (Finset (Fin n)) := powersetCard r range'k
Ccard : 𝒞.card = k.choose r
this : Set.Sized r ↑𝒞
B A : Finset (Fin n)
Ah : A ⊆ range'k ∧ A.card = r
BsubA : B ⊆ A
card_sdiff_i : (A \ B).card = i
⊢ r - i = B.card