-- Mathlib/Combinatorics/SimpleGraph/Triangle/Removal.lean
/-- **Triangle Removal Lemma**. If not all triangles can be removed by removing few edges (on the
order of `(card α)^2`), then there were many triangles to start with (on the order of
`(card α)^3`). -/
lemma FarFromTriangleFree.le_card_cliqueFinset (hG : G.FarFromTriangleFree ε) :
    triangleRemovalBound ε * card α ^ 3 ≤ #(G.cliqueFinset 3)

Proof state:
case inr.inr
α : Type u_1
inst✝² : DecidableEq α
inst✝¹ : Fintype α
G : SimpleGraph α
inst✝ : DecidableRel G.Adj
ε : ℝ
hG : G.FarFromTriangleFree ε
h✝ : Nonempty α
hε : 0 < ε
l : ℕ := ⌈4 / ε⌉₊
⊢ triangleRemovalBound ε * ↑(Fintype.card α) ^ 3 ≤ ↑(#(G.cliqueFinset 3))

Tactic:
have hl : 4/ε ≤ l := le_ceil (4/ε)

Result:
case inr.inr
α : Type u_1
inst✝² : DecidableEq α
inst✝¹ : Fintype α
G : SimpleGraph α
inst✝ : DecidableRel G.Adj
ε : ℝ
hG : G.FarFromTriangleFree ε
h✝ : Nonempty α
hε : 0 < ε
l : ℕ := ⌈4 / ε⌉₊
hl : 4 / ε ≤ ↑l
⊢ triangleRemovalBound ε * ↑(Fintype.card α) ^ 3 ≤ ↑(#(G.cliqueFinset 3))

Proof state:
case inr.inr
α : Type u_1
inst✝² : DecidableEq α
inst✝¹ : Fintype α
G : SimpleGraph α
inst✝ : DecidableRel G.Adj
ε : ℝ
hG : G.FarFromTriangleFree ε
h✝ : Nonempty α
hε : 0 < ε
⊢ triangleRemovalBound ε * ↑(Fintype.card α) ^ 3 ≤ ↑(#(G.cliqueFinset 3))

Tactic:
let l : ℕ := ⌈4 / ε⌉₊

Result:
case inr.inr
α : Type u_1
inst✝² : DecidableEq α
inst✝¹ : Fintype α
G : SimpleGraph α
inst✝ : DecidableRel G.Adj
ε : ℝ
hG : G.FarFromTriangleFree ε
h✝ : Nonempty α
hε : 0 < ε
l : ℕ := ⌈4 / ε⌉₊
⊢ triangleRemovalBound ε * ↑(Fintype.card α) ^ 3 ≤ ↑(#(G.cliqueFinset 3))

Proof state:
case inr.inr.inr.intro.intro.intro.intro.intro
α : Type u_1
inst✝² : DecidableEq α
inst✝¹ : Fintype α
G : SimpleGraph α
inst✝ : DecidableRel G.Adj
ε : ℝ
hG : G.FarFromTriangleFree ε
h✝ : Nonempty α
hε : 0 < ε
l : ℕ := ⌈4 / ε⌉₊
hl : 4 / ε ≤ ↑l
hl' : l ≤ Fintype.card α
P : Finpartition univ
hP₁ : P.IsEquipartition
hP₂ : l ≤ #P.parts
hP₃ : #P.parts ≤ bound (ε / 8) l
hP₄ : P.IsUniform G (ε / 8)
this : 4 / ε ≤ ↑(#P.parts)
k : ↑(#G.edgeFinset) - ↑(#(regularityReduced P G (ε / 8) (ε / 4)).edgeFinset) < ε * ↑(Fintype.card α ^ 2)
t : Finset α
ht : t ∈ (regularityReduced P G (ε / 8) (ε / 4)).cliqueFinset 3
⊢ triangleRemovalBound ε * ↑(Fintype.card α) ^ 3 ≤ ↑(#(G.cliqueFinset 3))

Tactic:
exact triangle_removal_aux hε hP₁ hP₃ ht

Result:
no goals

Proof state:
case a0
α : Type u_1
inst✝² : DecidableEq α
inst✝¹ : Fintype α
G : SimpleGraph α
inst✝ : DecidableRel G.Adj
ε : ℝ
hG : G.FarFromTriangleFree ε
h✝ : Nonempty α
hε : 0 < ε
l : ℕ := ⌈4 / ε⌉₊
hl : 4 / ε ≤ ↑l
hl' : Fintype.card α ≤ l
⊢ 0 ≤ triangleRemovalBound ε

Tactic:
exact (triangleRemovalBound_pos hε hG.lt_one.le).le

Result:
no goals

Proof state:
case inr.inr
α : Type u_1
inst✝² : DecidableEq α
inst✝¹ : Fintype α
G : SimpleGraph α
inst✝ : DecidableRel G.Adj
ε : ℝ
hG : G.FarFromTriangleFree ε
h✝ : Nonempty α
hε : 0 < ε
l : ℕ := ⌈4 / ε⌉₊
hl : 4 / ε ≤ ↑l
⊢ triangleRemovalBound ε * ↑(Fintype.card α) ^ 3 ≤ ↑(#(G.cliqueFinset 3))

Tactic:
rcases le_total (card α) l with hl' | hl'

Result:
case inr.inr.inl
α : Type u_1
inst✝² : DecidableEq α
inst✝¹ : Fintype α
G : SimpleGraph α
inst✝ : DecidableRel G.Adj
ε : ℝ
hG : G.FarFromTriangleFree ε
h✝ : Nonempty α
hε : 0 < ε
l : ℕ := ⌈4 / ε⌉₊
hl : 4 / ε ≤ ↑l
hl' : Fintype.card α ≤ l
⊢ triangleRemovalBound ε * ↑(Fintype.card α) ^ 3 ≤ ↑(#(G.cliqueFinset 3))

case inr.inr.inr
α : Type u_1
inst✝² : DecidableEq α
inst✝¹ : Fintype α
G : SimpleGraph α
inst✝ : DecidableRel G.Adj
ε : ℝ
hG : G.FarFromTriangleFree ε
h✝ : Nonempty α
hε : 0 < ε
l : ℕ := ⌈4 / ε⌉₊
hl : 4 / ε ≤ ↑l
hl' : l ≤ Fintype.card α
⊢ triangleRemovalBound ε * ↑(Fintype.card α) ^ 3 ≤ ↑(#(G.cliqueFinset 3))

Proof state:
case inr.inl
α : Type u_1
inst✝² : DecidableEq α
inst✝¹ : Fintype α
G : SimpleGraph α
inst✝ : DecidableRel G.Adj
ε : ℝ
hG : G.FarFromTriangleFree ε
h✝ : Nonempty α
hε : ε ≤ 0
⊢ triangleRemovalBound ε * ↑(Fintype.card α) ^ 3 ≤ ↑(#(G.cliqueFinset 3))

Tactic:
apply (mul_nonpos_of_nonpos_of_nonneg (triangleRemovalBound_nonpos hε) _).trans <;> positivity

Result:
no goals

Proof state:
case inr.inr.inr
α : Type u_1
inst✝² : DecidableEq α
inst✝¹ : Fintype α
G : SimpleGraph α
inst✝ : DecidableRel G.Adj
ε : ℝ
hG : G.FarFromTriangleFree ε
h✝ : Nonempty α
hε : 0 < ε
l : ℕ := ⌈4 / ε⌉₊
hl : 4 / ε ≤ ↑l
hl' : l ≤ Fintype.card α
⊢ triangleRemovalBound ε * ↑(Fintype.card α) ^ 3 ≤ ↑(#(G.cliqueFinset 3))

Tactic:
obtain ⟨P, hP₁, hP₂, hP₃, hP₄⟩ := szemeredi_regularity G (by positivity : 0 < ε / 8) hl'

Result:
case inr.inr.inr.intro.intro.intro.intro
α : Type u_1
inst✝² : DecidableEq α
inst✝¹ : Fintype α
G : SimpleGraph α
inst✝ : DecidableRel G.Adj
ε : ℝ
hG : G.FarFromTriangleFree ε
h✝ : Nonempty α
hε : 0 < ε
l : ℕ := ⌈4 / ε⌉₊
hl : 4 / ε ≤ ↑l
hl' : l ≤ Fintype.card α
P : Finpartition univ
hP₁ : P.IsEquipartition
hP₂ : l ≤ #P.parts
hP₃ : #P.parts ≤ bound (ε / 8) l
hP₄ : P.IsUniform G (ε / 8)
⊢ triangleRemovalBound ε * ↑(Fintype.card α) ^ 3 ≤ ↑(#(G.cliqueFinset 3))

Proof state:
case inr
α : Type u_1
inst✝² : DecidableEq α
inst✝¹ : Fintype α
G : SimpleGraph α
inst✝ : DecidableRel G.Adj
ε : ℝ
hG : G.FarFromTriangleFree ε
h✝ : Nonempty α
⊢ triangleRemovalBound ε * ↑(Fintype.card α) ^ 3 ≤ ↑(#(G.cliqueFinset 3))

Tactic:
obtain hε | hε := le_or_lt ε 0

Result:
case inr.inl
α : Type u_1
inst✝² : DecidableEq α
inst✝¹ : Fintype α
G : SimpleGraph α
inst✝ : DecidableRel G.Adj
ε : ℝ
hG : G.FarFromTriangleFree ε
h✝ : Nonempty α
hε : ε ≤ 0
⊢ triangleRemovalBound ε * ↑(Fintype.card α) ^ 3 ≤ ↑(#(G.cliqueFinset 3))

case inr.inr
α : Type u_1
inst✝² : DecidableEq α
inst✝¹ : Fintype α
G : SimpleGraph α
inst✝ : DecidableRel G.Adj
ε : ℝ
hG : G.FarFromTriangleFree ε
h✝ : Nonempty α
hε : 0 < ε
⊢ triangleRemovalBound ε * ↑(Fintype.card α) ^ 3 ≤ ↑(#(G.cliqueFinset 3))

Proof state:
case inr.inr.inl
α : Type u_1
inst✝² : DecidableEq α
inst✝¹ : Fintype α
G : SimpleGraph α
inst✝ : DecidableRel G.Adj
ε : ℝ
hG : G.FarFromTriangleFree ε
h✝ : Nonempty α
hε : 0 < ε
l : ℕ := ⌈4 / ε⌉₊
hl : 4 / ε ≤ ↑l
hl' : Fintype.card α ≤ l
⊢ triangleRemovalBound ε * ↑(Fintype.card α) ^ 3 ≤ ↑(#(G.cliqueFinset 3))

Tactic:
calc
  _ ≤ triangleRemovalBound ε * ↑l ^ 3 := by
    gcongr; exact (triangleRemovalBound_pos hε hG.lt_one.le).le
  _ ≤ (1 : ℝ) := (triangleRemovalBound_mul_cube_lt hε).le
  _ ≤ _ := by simpa [one_le_iff_ne_zero] using (hG.cliqueFinset_nonempty hε).card_pos.ne'

Result:
no goals

Proof state:
case inr.inr.inr.intro.intro.intro.intro
α : Type u_1
inst✝² : DecidableEq α
inst✝¹ : Fintype α
G : SimpleGraph α
inst✝ : DecidableRel G.Adj
ε : ℝ
hG : G.FarFromTriangleFree ε
h✝ : Nonempty α
hε : 0 < ε
l : ℕ := ⌈4 / ε⌉₊
hl : 4 / ε ≤ ↑l
hl' : l ≤ Fintype.card α
P : Finpartition univ
hP₁ : P.IsEquipartition
hP₂ : l ≤ #P.parts
hP₃ : #P.parts ≤ bound (ε / 8) l
hP₄ : P.IsUniform G (ε / 8)
this : 4 / ε ≤ ↑(#P.parts)
k : ↑(#G.edgeFinset) - ↑(#(regularityReduced P G (ε / 8) (ε / 4)).edgeFinset) < ε * ↑(Fintype.card α ^ 2)
⊢ triangleRemovalBound ε * ↑(Fintype.card α) ^ 3 ≤ ↑(#(G.cliqueFinset 3))

Tactic:
obtain ⟨t, ht⟩ := hG.cliqueFinset_nonempty' regularityReduced_le k

Result:
case inr.inr.inr.intro.intro.intro.intro.intro
α : Type u_1
inst✝² : DecidableEq α
inst✝¹ : Fintype α
G : SimpleGraph α
inst✝ : DecidableRel G.Adj
ε : ℝ
hG : G.FarFromTriangleFree ε
h✝ : Nonempty α
hε : 0 < ε
l : ℕ := ⌈4 / ε⌉₊
hl : 4 / ε ≤ ↑l
hl' : l ≤ Fintype.card α
P : Finpartition univ
hP₁ : P.IsEquipartition
hP₂ : l ≤ #P.parts
hP₃ : #P.parts ≤ bound (ε / 8) l
hP₄ : P.IsUniform G (ε / 8)
this : 4 / ε ≤ ↑(#P.parts)
k : ↑(#G.edgeFinset) - ↑(#(regularityReduced P G (ε / 8) (ε / 4)).edgeFinset) < ε * ↑(Fintype.card α ^ 2)
t : Finset α
ht : t ∈ (regularityReduced P G (ε / 8) (ε / 4)).cliqueFinset 3
⊢ triangleRemovalBound ε * ↑(Fintype.card α) ^ 3 ≤ ↑(#(G.cliqueFinset 3))