Module: Mathlib.Combinatorics.SetFamily.FourFunctions

Goal state before:
pp: α : Type u_1
β : Type u_2
inst✝⁴ : DecidableEq α
inst✝³ : CommSemiring β
inst✝² : LinearOrder β
inst✝¹ : IsStrictOrderedRing β
a : α
f₁ f₂ f₃ f₄ : Finset α → β
u : Finset α
inst✝ : ExistsAddOfLE β
hu : a ∉ u
h₁ : 0 ≤ f₁
h₂ : 0 ≤ f₂
h₃ : 0 ≤ f₃
h₄ : 0 ≤ f₄
h : ∀ ⦃s : Finset α⦄, s ⊆ insert a u → ∀ ⦃t : Finset α⦄, t ⊆ insert a u → f₁ s * f₂ t ≤ f₃ (s ∩ t) * f₄ (s ∪ t)
𝒜 ℬ : Finset (Finset α)
⊢ ∀ ⦃s : Finset α⦄,
    s ⊆ u →
      ∀ ⦃t : Finset α⦄,
        t ⊆ u → collapse 𝒜 a f₁ s * collapse ℬ a f₂ t ≤ collapse (𝒜 ⊼ ℬ) a f₃ (s ∩ t) * collapse (𝒜 ⊻ ℬ) a f₄ (s ∪ t)

Tactic:
by
  rintro s hsu t htu
  -- Gather a bunch of facts we'll need a lot
  have := hsu.trans <| subset_insert a _
  have := htu.trans <| subset_insert a _
  have := insert_subset_insert a hsu
  have := insert_subset_insert a htu
  have has := notMem_mono hsu hu
  have hat := notMem_mono htu hu
  have : a ∉ s ∩ t := notMem_mono (inter_subset_left.trans hsu) hu
  have := notMem_union.2 ⟨has, hat⟩
  rw [collapse_eq has]
  split_ifs
  · rw [collapse_eq hat]
    split_ifs
    · rw [collapse_of_mem ‹_› (inter_mem_infs ‹_› ‹_›) (inter_mem_infs ‹_› ‹_›) rfl
        (insert_inter_distrib _ _ _).symm, collapse_of_mem ‹_› (union_mem_sups ‹_› ‹_›)
        (union_mem_sups ‹_› ‹_›) rfl (insert_union_distrib _ _ _).symm]
      refine ineq (h₁ _) (h₁ _) (h₂ _) (h₂ _) (h₃ _) (h₃ _) (h₄ _) (h₄ _) (h ‹_› ‹_›) ?_ ?_ ?_
      · simpa [*] using h ‹insert a s ⊆ _› ‹t ⊆ _›
      · simpa [*] using h ‹s ⊆ _› ‹insert a t ⊆ _›
      · simpa [*] using h ‹insert a s ⊆ _› ‹insert a t ⊆ _›
    · rw [add_zero, add_mul]
      refine (add_le_add (h ‹_› ‹_›) <| h ‹_› ‹_›).trans ?_
      rw [collapse_of_mem ‹_› (union_mem_sups ‹_› ‹_›) (union_mem_sups ‹_› ‹_›) rfl
        (insert_union _ _ _), insert_inter_of_notMem ‹_›, ← mul_add]
      gcongr
      exacts [add_nonneg (h₄ _) <| h₄ _, le_collapse_of_mem ‹_› h₃ rfl <| inter_mem_infs ‹_› ‹_›]
    · rw [zero_add, add_mul]
      refine (add_le_add (h ‹_› ‹_›) <| h ‹_› ‹_›).trans ?_
      rw [collapse_of_mem ‹_› (inter_mem_infs ‹_› ‹_›) (inter_mem_infs ‹_› ‹_›)
        (inter_insert_of_notMem ‹_›) (insert_inter_distrib _ _ _).symm, union_insert,
        insert_union_distrib, ← add_mul]
      gcongr
      exacts [add_nonneg (h₃ _) <| h₃ _,
        le_collapse_of_insert_mem ‹_› h₄ (insert_union_distrib _ _ _).symm (union_mem_sups ‹_› ‹_›)]
    · rw [add_zero, mul_zero]
      exact mul_nonneg (collapse_nonneg h₃ _) <| collapse_nonneg h₄ _
  · rw [add_zero, collapse_eq hat, mul_add]
    split_ifs
    · refine (add_le_add (h ‹_› ‹_›) <| h ‹_› ‹_›).trans ?_
      rw [collapse_of_mem ‹_› (union_mem_sups ‹_› ‹_›) (union_mem_sups ‹_› ‹_›) rfl
        (union_insert _ _ _), inter_insert_of_notMem ‹_›, ← mul_add]
      gcongr
      · exact add_nonneg (h₄ _) (h₄ _)
      · exact le_collapse_of_mem ‹_› h₃ rfl <| inter_mem_infs ‹_› ‹_›
    · rw [mul_zero, add_zero]
      exact (h ‹_› ‹_›).trans <| mul_le_mul (le_collapse_of_mem ‹_› h₃ rfl <|
        inter_mem_infs ‹_› ‹_›) (le_collapse_of_mem ‹_› h₄ rfl <| union_mem_sups ‹_› ‹_›)
        (h₄ _) <| collapse_nonneg h₃ _
    · rw [mul_zero, zero_add]
      refine (h ‹_› ‹_›).trans <| mul_le_mul ?_ (le_collapse_of_insert_mem ‹_› h₄
        (union_insert _ _ _) <| union_mem_sups ‹_› ‹_›) (h₄ _) <| collapse_nonneg h₃ _
      exact le_collapse_of_mem (notMem_mono inter_subset_left ‹_›) h₃
        (inter_insert_of_notMem ‹_›) <| inter_mem_infs ‹_› ‹_›
    · simp_rw [mul_zero, add_zero]
      exact mul_nonneg (collapse_nonneg h₃ _) <| collapse_nonneg h₄ _
  · rw [zero_add, collapse_eq hat, mul_add]
    split_ifs
    · refine (add_le_add (h ‹_› ‹_›) <| h ‹_› ‹_›).trans ?_
      rw [collapse_of_mem ‹_› (inter_mem_infs ‹_› ‹_›) (inter_mem_infs ‹_› ‹_›)
        (insert_inter_of_notMem ‹_›) (insert_inter_distrib _ _ _).symm,
        insert_inter_of_notMem ‹_›, ← insert_inter_distrib, insert_union, insert_union_distrib,
        ← add_mul]
      gcongr
      · exact add_nonneg (h₃ _) (h₃ _)
      · exact le_collapse_of_insert_mem ‹_› h₄
          (insert_union_distrib _ _ _).symm <| union_mem_sups ‹_› ‹_›
    · rw [mul_zero, add_zero]
      refine (h ‹_› ‹_›).trans <| mul_le_mul (le_collapse_of_mem ‹_› h₃
        (insert_inter_of_notMem ‹_›) <| inter_mem_infs ‹_› ‹_›) (le_collapse_of_insert_mem ‹_› h₄
        (insert_union _ _ _) <| union_mem_sups ‹_› ‹_›) (h₄ _) <| collapse_nonneg h₃ _
    · rw [mul_zero, zero_add]
      exact (h ‹_› ‹_›).trans <| mul_le_mul (le_collapse_of_insert_mem ‹_› h₃
        (insert_inter_distrib _ _ _).symm <| inter_mem_infs ‹_› ‹_›) (le_collapse_of_insert_mem ‹_›
        h₄ (insert_union_distrib _ _ _).symm <| union_mem_sups ‹_› ‹_›) (h₄ _) <|
        collapse_nonneg h₃ _
    · simp_rw [mul_zero, add_zero]
      exact mul_nonneg (collapse_nonneg h₃ _) <| collapse_nonneg h₄ _
  · simp_rw [add_zero, zero_mul]
    exact mul_nonneg (collapse_nonneg h₃ _) <| collapse_nonneg h₄ _

Goal state after: