l3lab/ntp-mathlib huggingface dataset:
theorem subset_union_prime' {R : Type u} [CommRing R] {s : Finset ι} {f : ι → Ideal R} {a b : ι}
    (hp : ∀ i ∈ s, IsPrime (f i)) {I : Ideal R} :
    ((I : Set R) ⊆ f a ∪ f b ∪ ⋃ i ∈ (↑s : Set ι), f i) ↔ I ≤ f a ∨ I ≤ f b ∨ ∃ i ∈ s, I ≤ f i := by
  suffices
    ((I : Set R) ⊆ f a ∪ f b ∪ ⋃ i ∈ (↑s : Set ι), f i) → I ≤ f a ∨ I ≤ f b ∨ ∃ i ∈ s, I ≤ f i from
    ⟨this, fun h =>
      Or.casesOn h
        (fun h =>
          Set.Subset.trans h <|
            Set.Subset.trans (Set.subset_union_left _ _) (Set.subset_union_left _ _))
        fun h =>
        Or.casesOn h
          (fun h =>
            Set.Subset.trans h <|
              Set.Subset.trans (Set.subset_union_right _ _) (Set.subset_union_left _ _))
          fun ⟨i, his, hi⟩ => by
          refine' Set.Subset.trans hi <| Set.Subset.trans _ <| Set.subset_union_right _ _;
            exact Set.subset_biUnion_of_mem (u := fun x ↦ (f x : Set R)) (Finset.mem_coe.2 his)⟩
  generalize hn : s.card = n; intro h
  induction' n with n ih generalizing a b s
  · clear hp
    rw [Finset.card_eq_zero] at hn
    subst hn
    rw [Finset.coe_empty, Set.biUnion_empty, Set.union_empty, subset_union] at h
    simpa only [exists_prop, Finset.not_mem_empty, false_and_iff, exists_false, or_false_iff]
  classical
    replace hn : ∃ (i : ι) (t : Finset ι), i ∉ t ∧ insert i t = s ∧ t.card = n :=
      Finset.card_eq_succ.1 hn
    rcases hn with ⟨i, t, hit, rfl, hn⟩
    replace hp : IsPrime (f i) ∧ ∀ x ∈ t, IsPrime (f x) := (t.forall_mem_insert _ _).1 hp
    by_cases Ht : ∃ j ∈ t, f j ≤ f i
    · obtain ⟨j, hjt, hfji⟩ : ∃ j ∈ t, f j ≤ f i := Ht
      obtain ⟨u, hju, rfl⟩ : ∃ u, j ∉ u ∧ insert j u = t :=
        ⟨t.erase j, t.not_mem_erase j, Finset.insert_erase hjt⟩
      have hp' : ∀ k ∈ insert i u, IsPrime (f k) := by
        rw [Finset.forall_mem_insert] at hp ⊢
        exact ⟨hp.1, hp.2.2⟩
      have hiu : i ∉ u := mt Finset.mem_insert_of_mem hit
      have hn' : (insert i u).card = n := by
        rwa [Finset.card_insert_of_not_mem] at hn ⊢
        exacts [hiu, hju]
      have h' : (I : Set R) ⊆ f a ∪ f b ∪ ⋃ k ∈ (↑(insert i u) : Set ι), f k := by
        rw [Finset.coe_insert] at h ⊢
        rw [Finset.coe_insert] at h
        simp only [Set.biUnion_insert] at h ⊢
        rw [← Set.union_assoc (f i : Set R)] at h
        erw [Set.union_eq_self_of_subset_right hfji] at h
        

Proof state:
R✝ : Type u
ι : Type u_1
inst✝¹ : CommSemiring R✝
I✝ J K L : Ideal R✝
R : Type u
inst✝ : CommRing R
f : ι → Ideal R
I : Ideal R
n : ℕ
ih :
  ∀ {s : Finset ι} {a b : ι},
    (∀ i ∈ s, IsPrime (f i)) →
      Finset.card s = n → ↑I ⊆ ↑(f a) ∪ ↑(f b) ∪ ⋃ i ∈ ↑s, ↑(f i) → I ≤ f a ∨ I ≤ f b ∨ ∃ i ∈ s, I ≤ f i
a b i j : ι
hfji : f j ≤ f i
u : Finset ι
hju : j ∉ u
hit : i ∉ insert j u
hn : Finset.card (insert j u) = n
hp : IsPrime (f i) ∧ ∀ x ∈ insert j u, IsPrime (f x)
hjt : j ∈ insert j u
hp' : ∀ k ∈ insert i u, IsPrime (f k)
hiu : i ∉ u
hn' : Finset.card (insert i u) = n
h : ↑I ⊆ ↑(f a) ∪ ↑(f b) ∪ (↑(f i) ∪ ⋃ x ∈ ↑u, ↑(f x))
⊢ ↑I ⊆ ↑(f a) ∪ ↑(f b) ∪ (↑(f i) ∪ ⋃ x ∈ ↑u, ↑(f x))

Next tactic:
exact h
theorem subset_union_prime' {R : Type u} [CommRing R] {s : Finset ι} {f : ι → Ideal R} {a b : ι}
    (hp : ∀ i ∈ s, IsPrime (f i)) {I : Ideal R} :
    ((I : Set R) ⊆ f a ∪ f b ∪ ⋃ i ∈ (↑s : Set ι), f i) ↔ I ≤ f a ∨ I ≤ f b ∨ ∃ i ∈ s, I ≤ f i := by
  suffices
    ((I : Set R) ⊆ f a ∪ f b ∪ ⋃ i ∈ (↑s : Set ι), f i) → I ≤ f a ∨ I ≤ f b ∨ ∃ i ∈ s, I ≤ f i from
    ⟨this, fun h =>
      Or.casesOn h
        (fun h =>
          Set.Subset.trans h <|
            Set.Subset.trans (Set.subset_union_left _ _) (Set.subset_union_left _ _))
        fun h =>
        Or.casesOn h
          (fun h =>
            Set.Subset.trans h <|
              Set.Subset.trans (Set.subset_union_right _ _) (Set.subset_union_left _ _))
          fun ⟨i, his, hi⟩ => by
          refine' Set.Subset.trans hi <| Set.Subset.trans _ <| Set.subset_union_right _ _;
            exact Set.subset_biUnion_of_mem (u := fun x ↦ (f x : Set R)) (Finset.mem_coe.2 his)⟩
  generalize hn : s.card = n; intro h
  induction' n with n ih generalizing a b s
  · clear hp
    rw [Finset.card_eq_zero] at hn
    subst hn
    rw [Finset.coe_empty, Set.biUnion_empty, Set.union_empty, subset_union] at h
    simpa only [exists_prop, Finset.not_mem_empty, false_and_iff, exists_false, or_false_iff]
  classical
    replace hn : ∃ (i : ι) (t : Finset ι), i ∉ t ∧ insert i t = s ∧ t.card = n :=
      Finset.card_eq_succ.1 hn
    rcases hn with ⟨i, t, hit, rfl, hn⟩
    replace hp : IsPrime (f i) ∧ ∀ x ∈ t, IsPrime (f x) := (t.forall_mem_insert _ _).1 hp
    by_cases Ht : ∃ j ∈ t, f j ≤ f i
    · obtain ⟨j, hjt, hfji⟩ : ∃ j ∈ t, f j ≤ f i := Ht
      obtain ⟨u, hju, rfl⟩ : ∃ u, j ∉ u ∧ insert j u = t :=
        ⟨t.erase j, t.not_mem_erase j, Finset.insert_erase hjt⟩
      have hp' : ∀ k ∈ insert i u, IsPrime (f k) := by
        rw [Finset.forall_mem_insert] at hp ⊢
        exact ⟨hp.1, hp.2.2⟩
      have hiu : i ∉ u := mt Finset.mem_insert_of_mem hit
      have hn' : (insert i u).card = n := by
        rwa [Finset.card_insert_of_not_mem] at hn ⊢
        exacts [hiu, hju]
      have h' : (I : Set R) ⊆ f a ∪ f b ∪ ⋃ k ∈ (↑(insert i u) : Set ι), f k := by
        rw [Finset.coe_insert] at h ⊢
        rw [Finset.coe_insert] at h
        simp only [Set.biUnion_insert] at h ⊢
        rw [← Set.union_assoc (f i : Set R)] at h
        erw [Set.union_eq_self_of_subset_right hfji] at h
        exact h
      specialize ih hp' hn' h'
      

Proof state:
case pos.intro.intro.intro.intro
R✝ : Type u
ι : Type u_1
inst✝¹ : CommSemiring R✝
I✝ J K L : Ideal R✝
R : Type u
inst✝ : CommRing R
f : ι → Ideal R
I : Ideal R
n : ℕ
a b i j : ι
hfji : f j ≤ f i
u : Finset ι
hju : j ∉ u
hit : i ∉ insert j u
hn : Finset.card (insert j u) = n
h : ↑I ⊆ ↑(f a) ∪ ↑(f b) ∪ ⋃ i_1 ∈ ↑(insert i (insert j u)), ↑(f i_1)
hp : IsPrime (f i) ∧ ∀ x ∈ insert j u, IsPrime (f x)
hjt : j ∈ insert j u
hp' : ∀ k ∈ insert i u, IsPrime (f k)
hiu : i ∉ u
hn' : Finset.card (insert i u) = n
h' : ↑I ⊆ ↑(f a) ∪ ↑(f b) ∪ ⋃ k ∈ ↑(insert i u), ↑(f k)
ih : I ≤ f a ∨ I ≤ f b ∨ ∃ i_1 ∈ insert i u, I ≤ f i_1
⊢ I ≤ f a ∨ I ≤ f b ∨ ∃ i_1 ∈ insert i (insert j u), I ≤ f i_1

Next tactic:
refine' ih.imp id (Or.imp id (Exists.imp fun k => _))
theorem subset_union_prime' {R : Type u} [CommRing R] {s : Finset ι} {f : ι → Ideal R} {a b : ι}
    (hp : ∀ i ∈ s, IsPrime (f i)) {I : Ideal R} :
    ((I : Set R) ⊆ f a ∪ f b ∪ ⋃ i ∈ (↑s : Set ι), f i) ↔ I ≤ f a ∨ I ≤ f b ∨ ∃ i ∈ s, I ≤ f i := by
  suffices
    ((I : Set R) ⊆ f a ∪ f b ∪ ⋃ i ∈ (↑s : Set ι), f i) → I ≤ f a ∨ I ≤ f b ∨ ∃ i ∈ s, I ≤ f i from
    ⟨this, fun h =>
      Or.casesOn h
        (fun h =>
          Set.Subset.trans h <|
            Set.Subset.trans (Set.subset_union_left _ _) (Set.subset_union_left _ _))
        fun h =>
        Or.casesOn h
          (fun h =>
            Set.Subset.trans h <|
              Set.Subset.trans (Set.subset_union_right _ _) (Set.subset_union_left _ _))
          fun ⟨i, his, hi⟩ => by
          refine' Set.Subset.trans hi <| Set.Subset.trans _ <| Set.subset_union_right _ _;
            exact Set.subset_biUnion_of_mem (u := fun x ↦ (f x : Set R)) (Finset.mem_coe.2 his)⟩
  generalize hn : s.card = n; intro h
  induction' n with n ih generalizing a b s
  · clear hp
    rw [Finset.card_eq_zero] at hn
    subst hn
    rw [Finset.coe_empty, Set.biUnion_empty, Set.union_empty, subset_union] at h
    simpa only [exists_prop, Finset.not_mem_empty, false_and_iff, exists_false, or_false_iff]
  classical
    replace hn : ∃ (i : ι) (t : Finset ι), i ∉ t ∧ insert i t = s ∧ t.card = n :=
      Finset.card_eq_succ.1 hn
    rcases hn with ⟨i, t, hit, rfl, hn⟩
    replace hp : IsPrime (f i) ∧ ∀ x ∈ t, IsPrime (f x) := (t.forall_mem_insert _ _).1 hp
    by_cases Ht : ∃ j ∈ t, f j ≤ f i
    · obtain ⟨j, hjt, hfji⟩ : ∃ j ∈ t, f j ≤ f i := Ht
      obtain ⟨u, hju, rfl⟩ : ∃ u, j ∉ u ∧ insert j u = t :=
        ⟨t.erase j, t.not_mem_erase j, Finset.insert_erase hjt⟩
      have hp' : ∀ k ∈ insert i u, IsPrime (f k) := by
        rw [Finset.forall_mem_insert] at hp ⊢
        exact ⟨hp.1, hp.2.2⟩
      have hiu : i ∉ u := mt Finset.mem_insert_of_mem hit
      have hn' : (insert i u).card = n := by
        rwa [Finset.card_insert_of_not_mem] at hn ⊢
        exacts [hiu, hju]
      have h' : (I : Set R) ⊆ f a ∪ f b ∪ ⋃ k ∈ (↑(insert i u) : Set ι), f k := by
        rw [Finset.coe_insert] at h ⊢
        rw [Finset.coe_insert] at h
        simp only [Set.biUnion_insert] at h ⊢
        rw [← Set.union_assoc (f i : Set R)] at h
        erw [Set.union_eq_self_of_subset_right hfji] at h
        exact h
      specialize ih hp' hn' h'
      refine' ih.imp id (Or.imp id (Exists.imp fun k => _))
      exact And.imp (fun hk => Finset.insert_subset_insert i (Finset.subset_insert j u) hk) id
    

Proof state:
case neg
R✝ : Type u
ι : Type u_1
inst✝¹ : CommSemiring R✝
I✝ J K L : Ideal R✝
R : Type u
inst✝ : CommRing R
f : ι → Ideal R
I : Ideal R
n : ℕ
ih :
  ∀ {s : Finset ι} {a b : ι},
    (∀ i ∈ s, IsPrime (f i)) →
      Finset.card s = n → ↑I ⊆ ↑(f a) ∪ ↑(f b) ∪ ⋃ i ∈ ↑s, ↑(f i) → I ≤ f a ∨ I ≤ f b ∨ ∃ i ∈ s, I ≤ f i
a b i : ι
t : Finset ι
hit : i ∉ t
hn : Finset.card t = n
h : ↑I ⊆ ↑(f a) ∪ ↑(f b) ∪ ⋃ i_1 ∈ ↑(insert i t), ↑(f i_1)
hp : IsPrime (f i) ∧ ∀ x ∈ t, IsPrime (f x)
Ht : ¬∃ j ∈ t, f j ≤ f i
⊢ I ≤ f a ∨ I ≤ f b ∨ ∃ i_1 ∈ insert i t, I ≤ f i_1

Next tactic:
by_cases Ha : f a ≤ f i
/-- Prime avoidance. Atiyah-Macdonald 1.11, Eisenbud 3.3, Stacks 00DS, Matsumura Ex.1.6. -/
theorem subset_union_prime {R : Type u} [CommRing R] {s : Finset ι} {f : ι → Ideal R} (a b : ι)
    (hp : ∀ i ∈ s, i ≠ a → i ≠ b → IsPrime (f i)) {I : Ideal R} :
    ((I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i) ↔ ∃ i ∈ s, I ≤ f i :=
  suffices ((I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i) → ∃ i, i ∈ s ∧ I ≤ f i by
    have aux := fun h => (bex_def.2 <| this h)
    simp_rw [exists_prop] at aux
    refine ⟨aux, fun ⟨i, his, hi⟩ ↦ Set.Subset.trans hi ?_⟩
    apply Set.subset_biUnion_of_mem (show i ∈ (↑s : Set ι) from his)
  fun h : (I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i => by
  classical
    

Proof state:
R✝ : Type u
ι : Type u_1
inst✝¹ : CommSemiring R✝
I✝ J K L : Ideal R✝
R : Type u
inst✝ : CommRing R
s : Finset ι
f : ι → Ideal R
a b : ι
hp : ∀ i ∈ s, i ≠ a → i ≠ b → IsPrime (f i)
I : Ideal R
h : ↑I ⊆ ⋃ i ∈ ↑s, ↑(f i)
⊢ ∃ i ∈ s, I ≤ f i

Next tactic:
by_cases has : a ∈ s
/-- Prime avoidance. Atiyah-Macdonald 1.11, Eisenbud 3.3, Stacks 00DS, Matsumura Ex.1.6. -/
theorem subset_union_prime {R : Type u} [CommRing R] {s : Finset ι} {f : ι → Ideal R} (a b : ι)
    (hp : ∀ i ∈ s, i ≠ a → i ≠ b → IsPrime (f i)) {I : Ideal R} :
    ((I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i) ↔ ∃ i ∈ s, I ≤ f i :=
  suffices ((I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i) → ∃ i, i ∈ s ∧ I ≤ f i by
    have aux := fun h => (bex_def.2 <| this h)
    simp_rw [exists_prop] at aux
    refine ⟨aux, fun ⟨i, his, hi⟩ ↦ Set.Subset.trans hi ?_⟩
    apply Set.subset_biUnion_of_mem (show i ∈ (↑s : Set ι) from his)
  fun h : (I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i => by
  classical
    by_cases has : a ∈ s
    · 

Proof state:
case pos
R✝ : Type u
ι : Type u_1
inst✝¹ : CommSemiring R✝
I✝ J K L : Ideal R✝
R : Type u
inst✝ : CommRing R
s : Finset ι
f : ι → Ideal R
a b : ι
hp : ∀ i ∈ s, i ≠ a → i ≠ b → IsPrime (f i)
I : Ideal R
h : ↑I ⊆ ⋃ i ∈ ↑s, ↑(f i)
has : a ∈ s
⊢ ∃ i ∈ s, I ≤ f i

Next tactic:
obtain ⟨t, hat, rfl⟩ : ∃ t, a ∉ t ∧ insert a t = s :=
        ⟨s.erase a, Finset.not_mem_erase a s, Finset.insert_erase has⟩
/-- Prime avoidance. Atiyah-Macdonald 1.11, Eisenbud 3.3, Stacks 00DS, Matsumura Ex.1.6. -/
theorem subset_union_prime {R : Type u} [CommRing R] {s : Finset ι} {f : ι → Ideal R} (a b : ι)
    (hp : ∀ i ∈ s, i ≠ a → i ≠ b → IsPrime (f i)) {I : Ideal R} :
    ((I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i) ↔ ∃ i ∈ s, I ≤ f i :=
  suffices ((I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i) → ∃ i, i ∈ s ∧ I ≤ f i by
    have aux := fun h => (bex_def.2 <| this h)
    simp_rw [exists_prop] at aux
    refine ⟨aux, fun ⟨i, his, hi⟩ ↦ Set.Subset.trans hi ?_⟩
    apply Set.subset_biUnion_of_mem (show i ∈ (↑s : Set ι) from his)
  fun h : (I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i => by
  classical
    by_cases has : a ∈ s
    · obtain ⟨t, hat, rfl⟩ : ∃ t, a ∉ t ∧ insert a t = s :=
        ⟨s.erase a, Finset.not_mem_erase a s, Finset.insert_erase has⟩
      

Proof state:
case pos.intro.intro
R✝ : Type u
ι : Type u_1
inst✝¹ : CommSemiring R✝
I✝ J K L : Ideal R✝
R : Type u
inst✝ : CommRing R
f : ι → Ideal R
a b : ι
I : Ideal R
t : Finset ι
hat : a ∉ t
hp : ∀ i ∈ insert a t, i ≠ a → i ≠ b → IsPrime (f i)
h : ↑I ⊆ ⋃ i ∈ ↑(insert a t), ↑(f i)
has : a ∈ insert a t
⊢ ∃ i ∈ insert a t, I ≤ f i

Next tactic:
by_cases hbt : b ∈ t
/-- Prime avoidance. Atiyah-Macdonald 1.11, Eisenbud 3.3, Stacks 00DS, Matsumura Ex.1.6. -/
theorem subset_union_prime {R : Type u} [CommRing R] {s : Finset ι} {f : ι → Ideal R} (a b : ι)
    (hp : ∀ i ∈ s, i ≠ a → i ≠ b → IsPrime (f i)) {I : Ideal R} :
    ((I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i) ↔ ∃ i ∈ s, I ≤ f i :=
  suffices ((I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i) → ∃ i, i ∈ s ∧ I ≤ f i by
    have aux := fun h => (bex_def.2 <| this h)
    simp_rw [exists_prop] at aux
    refine ⟨aux, fun ⟨i, his, hi⟩ ↦ Set.Subset.trans hi ?_⟩
    apply Set.subset_biUnion_of_mem (show i ∈ (↑s : Set ι) from his)
  fun h : (I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i => by
  classical
    by_cases has : a ∈ s
    · obtain ⟨t, hat, rfl⟩ : ∃ t, a ∉ t ∧ insert a t = s :=
        ⟨s.erase a, Finset.not_mem_erase a s, Finset.insert_erase has⟩
      by_cases hbt : b ∈ t
      · 

Proof state:
case pos
R✝ : Type u
ι : Type u_1
inst✝¹ : CommSemiring R✝
I✝ J K L : Ideal R✝
R : Type u
inst✝ : CommRing R
f : ι → Ideal R
a b : ι
I : Ideal R
t : Finset ι
hat : a ∉ t
hp : ∀ i ∈ insert a t, i ≠ a → i ≠ b → IsPrime (f i)
h : ↑I ⊆ ⋃ i ∈ ↑(insert a t), ↑(f i)
has : a ∈ insert a t
hbt : b ∈ t
⊢ ∃ i ∈ insert a t, I ≤ f i

Next tactic:
obtain ⟨u, hbu, rfl⟩ : ∃ u, b ∉ u ∧ insert b u = t :=
          ⟨t.erase b, Finset.not_mem_erase b t, Finset.insert_erase hbt⟩
/-- Prime avoidance. Atiyah-Macdonald 1.11, Eisenbud 3.3, Stacks 00DS, Matsumura Ex.1.6. -/
theorem subset_union_prime {R : Type u} [CommRing R] {s : Finset ι} {f : ι → Ideal R} (a b : ι)
    (hp : ∀ i ∈ s, i ≠ a → i ≠ b → IsPrime (f i)) {I : Ideal R} :
    ((I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i) ↔ ∃ i ∈ s, I ≤ f i :=
  suffices ((I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i) → ∃ i, i ∈ s ∧ I ≤ f i by
    have aux := fun h => (bex_def.2 <| this h)
    simp_rw [exists_prop] at aux
    refine ⟨aux, fun ⟨i, his, hi⟩ ↦ Set.Subset.trans hi ?_⟩
    apply Set.subset_biUnion_of_mem (show i ∈ (↑s : Set ι) from his)
  fun h : (I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i => by
  classical
    by_cases has : a ∈ s
    · obtain ⟨t, hat, rfl⟩ : ∃ t, a ∉ t ∧ insert a t = s :=
        ⟨s.erase a, Finset.not_mem_erase a s, Finset.insert_erase has⟩
      by_cases hbt : b ∈ t
      · obtain ⟨u, hbu, rfl⟩ : ∃ u, b ∉ u ∧ insert b u = t :=
          ⟨t.erase b, Finset.not_mem_erase b t, Finset.insert_erase hbt⟩
        

Proof state:
case pos.intro.intro
R✝ : Type u
ι : Type u_1
inst✝¹ : CommSemiring R✝
I✝ J K L : Ideal R✝
R : Type u
inst✝ : CommRing R
f : ι → Ideal R
a b : ι
I : Ideal R
u : Finset ι
hbu : b ∉ u
hat : a ∉ insert b u
hp : ∀ i ∈ insert a (insert b u), i ≠ a → i ≠ b → IsPrime (f i)
h : ↑I ⊆ ⋃ i ∈ ↑(insert a (insert b u)), ↑(f i)
has : a ∈ insert a (insert b u)
hbt : b ∈ insert b u
⊢ ∃ i ∈ insert a (insert b u), I ≤ f i

Next tactic:
have hp' : ∀ i ∈ u, IsPrime (f i) := by
          intro i hiu
          refine' hp i (Finset.mem_insert_of_mem (Finset.mem_insert_of_mem hiu)) _ _ <;>
              rintro rfl <;>
            solve_by_elim only [Finset.mem_insert_of_mem, *]
/-- Prime avoidance. Atiyah-Macdonald 1.11, Eisenbud 3.3, Stacks 00DS, Matsumura Ex.1.6. -/
theorem subset_union_prime {R : Type u} [CommRing R] {s : Finset ι} {f : ι → Ideal R} (a b : ι)
    (hp : ∀ i ∈ s, i ≠ a → i ≠ b → IsPrime (f i)) {I : Ideal R} :
    ((I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i) ↔ ∃ i ∈ s, I ≤ f i :=
  suffices ((I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i) → ∃ i, i ∈ s ∧ I ≤ f i by
    have aux := fun h => (bex_def.2 <| this h)
    simp_rw [exists_prop] at aux
    refine ⟨aux, fun ⟨i, his, hi⟩ ↦ Set.Subset.trans hi ?_⟩
    apply Set.subset_biUnion_of_mem (show i ∈ (↑s : Set ι) from his)
  fun h : (I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i => by
  classical
    by_cases has : a ∈ s
    · obtain ⟨t, hat, rfl⟩ : ∃ t, a ∉ t ∧ insert a t = s :=
        ⟨s.erase a, Finset.not_mem_erase a s, Finset.insert_erase has⟩
      by_cases hbt : b ∈ t
      · obtain ⟨u, hbu, rfl⟩ : ∃ u, b ∉ u ∧ insert b u = t :=
          ⟨t.erase b, Finset.not_mem_erase b t, Finset.insert_erase hbt⟩
        have hp' : ∀ i ∈ u, IsPrime (f i) := by
          

Proof state:
R✝ : Type u
ι : Type u_1
inst✝¹ : CommSemiring R✝
I✝ J K L : Ideal R✝
R : Type u
inst✝ : CommRing R
f : ι → Ideal R
a b : ι
I : Ideal R
u : Finset ι
hbu : b ∉ u
hat : a ∉ insert b u
hp : ∀ i ∈ insert a (insert b u), i ≠ a → i ≠ b → IsPrime (f i)
h : ↑I ⊆ ⋃ i ∈ ↑(insert a (insert b u)), ↑(f i)
has : a ∈ insert a (insert b u)
hbt : b ∈ insert b u
⊢ ∀ i ∈ u, IsPrime (f i)

Next tactic:
intro i hiu
/-- Prime avoidance. Atiyah-Macdonald 1.11, Eisenbud 3.3, Stacks 00DS, Matsumura Ex.1.6. -/
theorem subset_union_prime {R : Type u} [CommRing R] {s : Finset ι} {f : ι → Ideal R} (a b : ι)
    (hp : ∀ i ∈ s, i ≠ a → i ≠ b → IsPrime (f i)) {I : Ideal R} :
    ((I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i) ↔ ∃ i ∈ s, I ≤ f i :=
  suffices ((I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i) → ∃ i, i ∈ s ∧ I ≤ f i by
    have aux := fun h => (bex_def.2 <| this h)
    simp_rw [exists_prop] at aux
    refine ⟨aux, fun ⟨i, his, hi⟩ ↦ Set.Subset.trans hi ?_⟩
    apply Set.subset_biUnion_of_mem (show i ∈ (↑s : Set ι) from his)
  fun h : (I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i => by
  classical
    by_cases has : a ∈ s
    · obtain ⟨t, hat, rfl⟩ : ∃ t, a ∉ t ∧ insert a t = s :=
        ⟨s.erase a, Finset.not_mem_erase a s, Finset.insert_erase has⟩
      by_cases hbt : b ∈ t
      · obtain ⟨u, hbu, rfl⟩ : ∃ u, b ∉ u ∧ insert b u = t :=
          ⟨t.erase b, Finset.not_mem_erase b t, Finset.insert_erase hbt⟩
        have hp' : ∀ i ∈ u, IsPrime (f i) := by
          intro i hiu
          

Proof state:
R✝ : Type u
ι : Type u_1
inst✝¹ : CommSemiring R✝
I✝ J K L : Ideal R✝
R : Type u
inst✝ : CommRing R
f : ι → Ideal R
a b : ι
I : Ideal R
u : Finset ι
hbu : b ∉ u
hat : a ∉ insert b u
hp : ∀ i ∈ insert a (insert b u), i ≠ a → i ≠ b → IsPrime (f i)
h : ↑I ⊆ ⋃ i ∈ ↑(insert a (insert b u)), ↑(f i)
has : a ∈ insert a (insert b u)
hbt : b ∈ insert b u
i : ι
hiu : i ∈ u
⊢ IsPrime (f i)

Next tactic:
refine' hp i (Finset.mem_insert_of_mem (Finset.mem_insert_of_mem hiu)) _ _
/-- Prime avoidance. Atiyah-Macdonald 1.11, Eisenbud 3.3, Stacks 00DS, Matsumura Ex.1.6. -/
theorem subset_union_prime {R : Type u} [CommRing R] {s : Finset ι} {f : ι → Ideal R} (a b : ι)
    (hp : ∀ i ∈ s, i ≠ a → i ≠ b → IsPrime (f i)) {I : Ideal R} :
    ((I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i) ↔ ∃ i ∈ s, I ≤ f i :=
  suffices ((I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i) → ∃ i, i ∈ s ∧ I ≤ f i by
    have aux := fun h => (bex_def.2 <| this h)
    simp_rw [exists_prop] at aux
    refine ⟨aux, fun ⟨i, his, hi⟩ ↦ Set.Subset.trans hi ?_⟩
    apply Set.subset_biUnion_of_mem (show i ∈ (↑s : Set ι) from his)
  fun h : (I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i => by
  classical
    by_cases has : a ∈ s
    · obtain ⟨t, hat, rfl⟩ : ∃ t, a ∉ t ∧ insert a t = s :=
        ⟨s.erase a, Finset.not_mem_erase a s, Finset.insert_erase has⟩
      by_cases hbt : b ∈ t
      · obtain ⟨u, hbu, rfl⟩ : ∃ u, b ∉ u ∧ insert b u = t :=
          ⟨t.erase b, Finset.not_mem_erase b t, Finset.insert_erase hbt⟩
        have hp' : ∀ i ∈ u, IsPrime (f i) := by
          intro i hiu
          refine' hp i (Finset.mem_insert_of_mem (Finset.mem_insert_of_mem hiu)) _ _ <;>
              

Proof state:
case refine'_1
R✝ : Type u
ι : Type u_1
inst✝¹ : CommSemiring R✝
I✝ J K L : Ideal R✝
R : Type u
inst✝ : CommRing R
f : ι → Ideal R
a b : ι
I : Ideal R
u : Finset ι
hbu : b ∉ u
hat : a ∉ insert b u
hp : ∀ i ∈ insert a (insert b u), i ≠ a → i ≠ b → IsPrime (f i)
h : ↑I ⊆ ⋃ i ∈ ↑(insert a (insert b u)), ↑(f i)
has : a ∈ insert a (insert b u)
hbt : b ∈ insert b u
i : ι
hiu : i ∈ u
⊢ i ≠ a

Next tactic:
rintro rfl
/-- Prime avoidance. Atiyah-Macdonald 1.11, Eisenbud 3.3, Stacks 00DS, Matsumura Ex.1.6. -/
theorem subset_union_prime {R : Type u} [CommRing R] {s : Finset ι} {f : ι → Ideal R} (a b : ι)
    (hp : ∀ i ∈ s, i ≠ a → i ≠ b → IsPrime (f i)) {I : Ideal R} :
    ((I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i) ↔ ∃ i ∈ s, I ≤ f i :=
  suffices ((I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i) → ∃ i, i ∈ s ∧ I ≤ f i by
    have aux := fun h => (bex_def.2 <| this h)
    simp_rw [exists_prop] at aux
    refine ⟨aux, fun ⟨i, his, hi⟩ ↦ Set.Subset.trans hi ?_⟩
    apply Set.subset_biUnion_of_mem (show i ∈ (↑s : Set ι) from his)
  fun h : (I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i => by
  classical
    by_cases has : a ∈ s
    · obtain ⟨t, hat, rfl⟩ : ∃ t, a ∉ t ∧ insert a t = s :=
        ⟨s.erase a, Finset.not_mem_erase a s, Finset.insert_erase has⟩
      by_cases hbt : b ∈ t
      · obtain ⟨u, hbu, rfl⟩ : ∃ u, b ∉ u ∧ insert b u = t :=
          ⟨t.erase b, Finset.not_mem_erase b t, Finset.insert_erase hbt⟩
        have hp' : ∀ i ∈ u, IsPrime (f i) := by
          intro i hiu
          refine' hp i (Finset.mem_insert_of_mem (Finset.mem_insert_of_mem hiu)) _ _ <;>
              

Proof state:
case refine'_2
R✝ : Type u
ι : Type u_1
inst✝¹ : CommSemiring R✝
I✝ J K L : Ideal R✝
R : Type u
inst✝ : CommRing R
f : ι → Ideal R
a b : ι
I : Ideal R
u : Finset ι
hbu : b ∉ u
hat : a ∉ insert b u
hp : ∀ i ∈ insert a (insert b u), i ≠ a → i ≠ b → IsPrime (f i)
h : ↑I ⊆ ⋃ i ∈ ↑(insert a (insert b u)), ↑(f i)
has : a ∈ insert a (insert b u)
hbt : b ∈ insert b u
i : ι
hiu : i ∈ u
⊢ i ≠ b

Next tactic:
rintro rfl
/-- Prime avoidance. Atiyah-Macdonald 1.11, Eisenbud 3.3, Stacks 00DS, Matsumura Ex.1.6. -/
theorem subset_union_prime {R : Type u} [CommRing R] {s : Finset ι} {f : ι → Ideal R} (a b : ι)
    (hp : ∀ i ∈ s, i ≠ a → i ≠ b → IsPrime (f i)) {I : Ideal R} :
    ((I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i) ↔ ∃ i ∈ s, I ≤ f i :=
  suffices ((I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i) → ∃ i, i ∈ s ∧ I ≤ f i by
    have aux := fun h => (bex_def.2 <| this h)
    simp_rw [exists_prop] at aux
    refine ⟨aux, fun ⟨i, his, hi⟩ ↦ Set.Subset.trans hi ?_⟩
    apply Set.subset_biUnion_of_mem (show i ∈ (↑s : Set ι) from his)
  fun h : (I : Set R) ⊆ ⋃ i ∈ (↑s : Set ι), f i => by
  classical
    by_cases has : a ∈ s
    · obtain ⟨t, hat, rfl⟩ : ∃ t, a ∉ t ∧ insert a t = s :=
        ⟨s.erase a, Finset.not_mem_erase a s, Finset.insert_erase has⟩
      by_cases hbt : b ∈ t
      · obtain ⟨u, hbu, rfl⟩ : ∃ u, b ∉ u ∧ insert b u = t :=
          ⟨t.erase b, Finset.not_mem_erase b t, Finset.insert_erase hbt⟩
        have hp' : ∀ i ∈ u, IsPrime (f i) := by
          intro i hiu
          refine' hp i (Finset.mem_insert_of_mem (Finset.mem_insert_of_mem hiu)) _ _ <;>
              rintro rfl <;>
            

Proof state:
case refine'_1
R✝ : Type u
ι : Type u_1
inst✝¹ : CommSemiring R✝
I✝ J K L : Ideal R✝
R : Type u
inst✝ : CommRing R
f : ι → Ideal R
b : ι
I : Ideal R
u : Finset ι
hbu : b ∉ u
hbt : b ∈ insert b u
i : ι
hiu : i ∈ u
hat : i ∉ insert b u
hp : ∀ i_1 ∈ insert i (insert b u), i_1 ≠ i → i_1 ≠ b → IsPrime (f i_1)
h : ↑I ⊆ ⋃ i_1 ∈ ↑(insert i (insert b u)), ↑(f i_1)
has : i ∈ insert i (insert b u)
⊢ False

Next tactic:
solve_by_elim only [Finset.mem_insert_of_mem, *]