-- Mathlib/Combinatorics/SetFamily/KruskalKatona.lean
theorem kruskal_katona (h𝒜r : (𝒜 : Set (Finset (Fin n))).Sized r) (h𝒞𝒜 : #𝒞 ≤ #𝒜)
    (h𝒞 : IsInitSeg 𝒞 r) : #(∂ 𝒞) ≤ #(∂ 𝒜)

Proof state:
n r : ℕ
𝒜 𝒞 : Finset (Finset (Fin n))
h𝒜r : Set.Sized r ↑𝒜
h𝒞𝒜 : #𝒞 ≤ #𝒜
h𝒞 : IsInitSeg 𝒞 r
⊢ #(∂ 𝒞) ≤ #(∂ 𝒜)

Tactic:
obtain ⟨𝒜', h𝒜, h𝒜𝒞⟩ := exists_subset_card_eq h𝒞𝒜

Result:
case intro.intro
n r : ℕ
𝒜 𝒞 : Finset (Finset (Fin n))
h𝒜r : Set.Sized r ↑𝒜
h𝒞𝒜 : #𝒞 ≤ #𝒜
h𝒞 : IsInitSeg 𝒞 r
𝒜' : Finset (Finset (Fin n))
h𝒜 : 𝒜' ⊆ 𝒜
h𝒜𝒞 : #𝒜' = #𝒞
⊢ #(∂ 𝒞) ≤ #(∂ 𝒜)

Proof state:
case intro.intro.intro.intro.intro.intro
n r : ℕ
𝒜 𝒞 : Finset (Finset (Fin n))
h𝒜r : Set.Sized r ↑𝒜
h𝒞𝒜 : #𝒞 ≤ #𝒜
h𝒞 : IsInitSeg 𝒞 r
𝒜' : Finset (Finset (Fin n))
h𝒜 : 𝒜' ⊆ 𝒜
h𝒜𝒞 : #𝒜' = #𝒞
ℬ : Finset (Finset (Fin n))
hℬ𝒜 : #(∂ ℬ) ≤ #(∂ 𝒜')
h𝒜ℬ : #𝒜' = #ℬ
hℬr : Set.Sized r ↑ℬ
hℬ : ∀ (U V : Finset (Fin n)), Finset.UV.UsefulCompression U V → IsCompressed U V ℬ
⊢ ℬ = 𝒞

Tactic:
have hcard : #ℬ = #𝒞 := h𝒜ℬ.symm.trans h𝒜𝒞

Result:
case intro.intro.intro.intro.intro.intro
n r : ℕ
𝒜 𝒞 : Finset (Finset (Fin n))
h𝒜r : Set.Sized r ↑𝒜
h𝒞𝒜 : #𝒞 ≤ #𝒜
h𝒞 : IsInitSeg 𝒞 r
𝒜' : Finset (Finset (Fin n))
h𝒜 : 𝒜' ⊆ 𝒜
h𝒜𝒞 : #𝒜' = #𝒞
ℬ : Finset (Finset (Fin n))
hℬ𝒜 : #(∂ ℬ) ≤ #(∂ 𝒜')
h𝒜ℬ : #𝒜' = #ℬ
hℬr : Set.Sized r ↑ℬ
hℬ : ∀ (U V : Finset (Fin n)), Finset.UV.UsefulCompression U V → IsCompressed U V ℬ
hcard : #ℬ = #𝒞
⊢ ℬ = 𝒞

Proof state:
n r : ℕ
𝒜 𝒞 : Finset (Finset (Fin n))
h𝒜r : Set.Sized r ↑𝒜
h𝒞𝒜 : #𝒞 ≤ #𝒜
h𝒞 : IsInitSeg 𝒞 r
𝒜' : Finset (Finset (Fin n))
h𝒜 : 𝒜' ⊆ 𝒜
h𝒜𝒞 : #𝒜' = #𝒞
ℬ : Finset (Finset (Fin n))
hℬ𝒜 : #(∂ ℬ) ≤ #(∂ 𝒜')
h𝒜ℬ : #𝒜' = #ℬ
hℬr : Set.Sized r ↑ℬ
hℬ : ∀ (U V : Finset (Fin n)), Finset.UV.UsefulCompression U V → IsCompressed U V ℬ
this : ℬ = 𝒞
⊢ #(∂ 𝒞) ≤ #(∂ 𝒜)

Tactic:
subst 𝒞

Result:
n r : ℕ
𝒜 : Finset (Finset (Fin n))
h𝒜r : Set.Sized r ↑𝒜
𝒜' : Finset (Finset (Fin n))
h𝒜 : 𝒜' ⊆ 𝒜
ℬ : Finset (Finset (Fin n))
hℬ𝒜 : #(∂ ℬ) ≤ #(∂ 𝒜')
h𝒜ℬ : #𝒜' = #ℬ
hℬr : Set.Sized r ↑ℬ
hℬ : ∀ (U V : Finset (Fin n)), Finset.UV.UsefulCompression U V → IsCompressed U V ℬ
h𝒞𝒜 : #ℬ ≤ #𝒜
h𝒞 : IsInitSeg ℬ r
h𝒜𝒞 : #𝒜' = #ℬ
⊢ #(∂ ℬ) ≤ #(∂ 𝒜)

Proof state:
n r : ℕ
𝒜 𝒞 : Finset (Finset (Fin n))
h𝒜r : Set.Sized r ↑𝒜
h𝒞𝒜 : #𝒞 ≤ #𝒜
h𝒞 : IsInitSeg 𝒞 r
𝒜' : Finset (Finset (Fin n))
h𝒜 : 𝒜' ⊆ 𝒜
h𝒜𝒞 : #𝒜' = #𝒞
⊢ ↑𝒜' ⊆ ↑𝒜

Tactic:
gcongr

Result:
no goals

Proof state:
case intro.intro.intro.intro.intro.intro
n r : ℕ
𝒜 𝒞 : Finset (Finset (Fin n))
h𝒜r : Set.Sized r ↑𝒜
h𝒞𝒜 : #𝒞 ≤ #𝒜
h𝒞 : IsInitSeg 𝒞 r
𝒜' : Finset (Finset (Fin n))
h𝒜 : 𝒜' ⊆ 𝒜
h𝒜𝒞 : #𝒜' = #𝒞
ℬ : Finset (Finset (Fin n))
hℬ𝒜 : #(∂ ℬ) ≤ #(∂ 𝒜')
h𝒜ℬ : #𝒜' = #ℬ
hℬr : Set.Sized r ↑ℬ
hℬ : ∀ (U V : Finset (Fin n)), Finset.UV.UsefulCompression U V → IsCompressed U V ℬ
hcard : #ℬ = #𝒞
⊢ ℬ = 𝒞

Tactic:
obtain h𝒞ℬ | hℬ𝒞 := h𝒞.total (UV.isInitSeg_of_compressed hℬr hℬ)

Result:
case intro.intro.intro.intro.intro.intro.inl
n r : ℕ
𝒜 𝒞 : Finset (Finset (Fin n))
h𝒜r : Set.Sized r ↑𝒜
h𝒞𝒜 : #𝒞 ≤ #𝒜
h𝒞 : IsInitSeg 𝒞 r
𝒜' : Finset (Finset (Fin n))
h𝒜 : 𝒜' ⊆ 𝒜
h𝒜𝒞 : #𝒜' = #𝒞
ℬ : Finset (Finset (Fin n))
hℬ𝒜 : #(∂ ℬ) ≤ #(∂ 𝒜')
h𝒜ℬ : #𝒜' = #ℬ
hℬr : Set.Sized r ↑ℬ
hℬ : ∀ (U V : Finset (Fin n)), Finset.UV.UsefulCompression U V → IsCompressed U V ℬ
hcard : #ℬ = #𝒞
h𝒞ℬ : 𝒞 ⊆ ℬ
⊢ ℬ = 𝒞

case intro.intro.intro.intro.intro.intro.inr
n r : ℕ
𝒜 𝒞 : Finset (Finset (Fin n))
h𝒜r : Set.Sized r ↑𝒜
h𝒞𝒜 : #𝒞 ≤ #𝒜
h𝒞 : IsInitSeg 𝒞 r
𝒜' : Finset (Finset (Fin n))
h𝒜 : 𝒜' ⊆ 𝒜
h𝒜𝒞 : #𝒜' = #𝒞
ℬ : Finset (Finset (Fin n))
hℬ𝒜 : #(∂ ℬ) ≤ #(∂ 𝒜')
h𝒜ℬ : #𝒜' = #ℬ
hℬr : Set.Sized r ↑ℬ
hℬ : ∀ (U V : Finset (Fin n)), Finset.UV.UsefulCompression U V → IsCompressed U V ℬ
hcard : #ℬ = #𝒞
hℬ𝒞 : ℬ ⊆ 𝒞
⊢ ℬ = 𝒞

Proof state:
n r : ℕ
𝒜 : Finset (Finset (Fin n))
h𝒜r : Set.Sized r ↑𝒜
𝒜' : Finset (Finset (Fin n))
h𝒜 : 𝒜' ⊆ 𝒜
ℬ : Finset (Finset (Fin n))
hℬ𝒜 : #(∂ ℬ) ≤ #(∂ 𝒜')
h𝒜ℬ : #𝒜' = #ℬ
hℬr : Set.Sized r ↑ℬ
hℬ : ∀ (U V : Finset (Fin n)), Finset.UV.UsefulCompression U V → IsCompressed U V ℬ
h𝒞𝒜 : #ℬ ≤ #𝒜
h𝒞 : IsInitSeg ℬ r
h𝒜𝒞 : #𝒜' = #ℬ
⊢ #(∂ ℬ) ≤ #(∂ 𝒜)

Tactic:
exact hℬ𝒜.trans (by gcongr)

Result:
no goals

Proof state:
n r : ℕ
𝒜 : Finset (Finset (Fin n))
h𝒜r : Set.Sized r ↑𝒜
𝒜' : Finset (Finset (Fin n))
h𝒜 : 𝒜' ⊆ 𝒜
ℬ : Finset (Finset (Fin n))
hℬ𝒜 : #(∂ ℬ) ≤ #(∂ 𝒜')
h𝒜ℬ : #𝒜' = #ℬ
hℬr : Set.Sized r ↑ℬ
hℬ : ∀ (U V : Finset (Fin n)), Finset.UV.UsefulCompression U V → IsCompressed U V ℬ
h𝒞𝒜 : #ℬ ≤ #𝒜
h𝒞 : IsInitSeg ℬ r
h𝒜𝒞 : #𝒜' = #ℬ
⊢ #(∂ 𝒜') ≤ #(∂ 𝒜)

Tactic:
gcongr

Result:
no goals

Proof state:
case intro.intro.intro.intro.intro.intro.inl
n r : ℕ
𝒜 𝒞 : Finset (Finset (Fin n))
h𝒜r : Set.Sized r ↑𝒜
h𝒞𝒜 : #𝒞 ≤ #𝒜
h𝒞 : IsInitSeg 𝒞 r
𝒜' : Finset (Finset (Fin n))
h𝒜 : 𝒜' ⊆ 𝒜
h𝒜𝒞 : #𝒜' = #𝒞
ℬ : Finset (Finset (Fin n))
hℬ𝒜 : #(∂ ℬ) ≤ #(∂ 𝒜')
h𝒜ℬ : #𝒜' = #ℬ
hℬr : Set.Sized r ↑ℬ
hℬ : ∀ (U V : Finset (Fin n)), Finset.UV.UsefulCompression U V → IsCompressed U V ℬ
hcard : #ℬ = #𝒞
h𝒞ℬ : 𝒞 ⊆ ℬ
⊢ ℬ = 𝒞

Tactic:
exact (eq_of_subset_of_card_le h𝒞ℬ hcard.le).symm

Result:
no goals

Proof state:
case intro.intro.intro.intro.intro.intro
n r : ℕ
𝒜 𝒞 : Finset (Finset (Fin n))
h𝒜r : Set.Sized r ↑𝒜
h𝒞𝒜 : #𝒞 ≤ #𝒜
h𝒞 : IsInitSeg 𝒞 r
𝒜' : Finset (Finset (Fin n))
h𝒜 : 𝒜' ⊆ 𝒜
h𝒜𝒞 : #𝒜' = #𝒞
ℬ : Finset (Finset (Fin n))
hℬ𝒜 : #(∂ ℬ) ≤ #(∂ 𝒜')
h𝒜ℬ : #𝒜' = #ℬ
hℬr : Set.Sized r ↑ℬ
hℬ : ∀ (U V : Finset (Fin n)), Finset.UV.UsefulCompression U V → IsCompressed U V ℬ
⊢ #(∂ 𝒞) ≤ #(∂ 𝒜)

Tactic:
suffices ℬ = 𝒞 by subst 𝒞; exact hℬ𝒜.trans (by gcongr)

Result:
case intro.intro.intro.intro.intro.intro
n r : ℕ
𝒜 𝒞 : Finset (Finset (Fin n))
h𝒜r : Set.Sized r ↑𝒜
h𝒞𝒜 : #𝒞 ≤ #𝒜
h𝒞 : IsInitSeg 𝒞 r
𝒜' : Finset (Finset (Fin n))
h𝒜 : 𝒜' ⊆ 𝒜
h𝒜𝒞 : #𝒜' = #𝒞
ℬ : Finset (Finset (Fin n))
hℬ𝒜 : #(∂ ℬ) ≤ #(∂ 𝒜')
h𝒜ℬ : #𝒜' = #ℬ
hℬr : Set.Sized r ↑ℬ
hℬ : ∀ (U V : Finset (Fin n)), Finset.UV.UsefulCompression U V → IsCompressed U V ℬ
⊢ ℬ = 𝒞

Proof state:
case intro.intro
n r : ℕ
𝒜 𝒞 : Finset (Finset (Fin n))
h𝒜r : Set.Sized r ↑𝒜
h𝒞𝒜 : #𝒞 ≤ #𝒜
h𝒞 : IsInitSeg 𝒞 r
𝒜' : Finset (Finset (Fin n))
h𝒜 : 𝒜' ⊆ 𝒜
h𝒜𝒞 : #𝒜' = #𝒞
⊢ #(∂ 𝒞) ≤ #(∂ 𝒜)

Tactic:
obtain ⟨ℬ, hℬ𝒜, h𝒜ℬ, hℬr, hℬ⟩ := UV.kruskal_katona_helper 𝒜' (h𝒜r.mono (by gcongr))

Result:
case intro.intro.intro.intro.intro.intro
n r : ℕ
𝒜 𝒞 : Finset (Finset (Fin n))
h𝒜r : Set.Sized r ↑𝒜
h𝒞𝒜 : #𝒞 ≤ #𝒜
h𝒞 : IsInitSeg 𝒞 r
𝒜' : Finset (Finset (Fin n))
h𝒜 : 𝒜' ⊆ 𝒜
h𝒜𝒞 : #𝒜' = #𝒞
ℬ : Finset (Finset (Fin n))
hℬ𝒜 : #(∂ ℬ) ≤ #(∂ 𝒜')
h𝒜ℬ : #𝒜' = #ℬ
hℬr : Set.Sized r ↑ℬ
hℬ : ∀ (U V : Finset (Fin n)), Finset.UV.UsefulCompression U V → IsCompressed U V ℬ
⊢ #(∂ 𝒞) ≤ #(∂ 𝒜)

Proof state:
case intro.intro.intro.intro.intro.intro.inr
n r : ℕ
𝒜 𝒞 : Finset (Finset (Fin n))
h𝒜r : Set.Sized r ↑𝒜
h𝒞𝒜 : #𝒞 ≤ #𝒜
h𝒞 : IsInitSeg 𝒞 r
𝒜' : Finset (Finset (Fin n))
h𝒜 : 𝒜' ⊆ 𝒜
h𝒜𝒞 : #𝒜' = #𝒞
ℬ : Finset (Finset (Fin n))
hℬ𝒜 : #(∂ ℬ) ≤ #(∂ 𝒜')
h𝒜ℬ : #𝒜' = #ℬ
hℬr : Set.Sized r ↑ℬ
hℬ : ∀ (U V : Finset (Fin n)), Finset.UV.UsefulCompression U V → IsCompressed U V ℬ
hcard : #ℬ = #𝒞
hℬ𝒞 : ℬ ⊆ 𝒞
⊢ ℬ = 𝒞

Tactic:
exact eq_of_subset_of_card_le hℬ𝒞 hcard.ge

Result:
no goals