Module: Mathlib.RingTheory.Spectrum.Prime.ChevalleyComplexity

Goal state before:
pp: case refine_1
R₀ : Type u_1
inst✝² : CommRing R₀
n : ℕ
R : Type u_6
inst✝¹ : CommRing R
inst✝ : Algebra R₀ R
c : R
i : Fin n
e : InductionObj R n
hi : c = (e.val i).leadingCoeff
hc : c ≠ 0
q₁ : R →ₐ[R₀] Localization.Away c := IsScalarTower.toAlgHom R₀ R (Localization.Away c)
q₂ : R →ₐ[R₀] R ⧸ Ideal.span {c} := Ideal.Quotient.mkₐ R₀ (Ideal.span {c})
q₂_surjective : Surjective ⇑q₂
e₁ : InductionObj (Localization.Away c) n :=
  { val := Polynomial.C (IsLocalization.Away.invSelf c) • ⇑(mapRingHom ↑q₁) ∘ e.val }
e₂ : InductionObj (R ⧸ Ideal.span {c}) n := { val := ⇑(mapRingHom ↑q₂) ∘ e.val }
degBound_e₁_le : e₁.degBound ≤ e.degBound
degBound_e₂_lt : e₂.degBound < e.degBound
H₁ : Statement R₀ (Localization.Away c) n e₁
H₂ : Statement R₀ (R ⧸ Ideal.span {c}) n e₂
f : R[X]
T₁ : ConstructibleSetData (Localization.Away c)
T₂ : ConstructibleSetData (R ⧸ Ideal.span {c})
hT₁ : comap Polynomial.C '' (zeroLocus (Set.range e₁.val) \ zeroLocus {(mapRingHom ↑q₁) f}) = T₁.toSet
hT₁deg : ∀ x ∈ T₁, x.n ≤ e₁.degBound
hT₂ : comap Polynomial.C '' (zeroLocus (Set.range e₂.val) \ zeroLocus {(mapRingHom ↑q₂) f}) = T₂.toSet
hT₂deg : ∀ x ∈ T₂, x.n ≤ e₂.degBound
x✝ : Invertible (q₁ c) := { invOf := IsLocalization.Away.invSelf c, invOf_mul_self := ⋯, mul_invOf_self := ⋯ }
he₁span :
  coeffSubmodule R₀ e₁ ^ e₁.powBound =
    ⅟(q₁ c ^ e₁.powBound) • Submodule.map q₁.toLinearMap (span R₀ ({c} ∪ ⋃ i, coeff(e.val i)) ^ e₁.powBound)
g₁ : (x : BasicConstructibleSetData (Localization.Away c)) → Fin x.n → R
hg₁ : ∀ x ∈ T₁, ∀ (i : Fin x.n), g₁ x i ∈ ↑(span R₀ ({c} ∪ ⋃ i, coeff(e.val i)) ^ e₁.powBound)
hq₁g₁ : ∀ x ∈ T₁, ∀ (i : Fin x.n), q₁.toLinearMap (g₁ x i) = q₁ c ^ e₁.powBound * x.g i
n₁ : Localization.Away c → ℕ
f₁ : Localization.Away c → R
hf₁ : ∀ (x : Localization.Away c), x * q₁ c ^ n₁ x = q₁ (f₁ x)
g₂ : (x : BasicConstructibleSetData (R ⧸ Ideal.span {c})) → Fin x.n → R
hg₂ : ∀ x ∈ T₂, ∀ (i : Fin x.n), g₂ x i ∈ ↑(coeffSubmodule R₀ e ^ e₂.powBound)
hq₂g₂ : ∀ x ∈ T₂, ∀ (i : Fin x.n), q₂.toLinearMap (g₂ x i) = x.g i
f₂ : R ⧸ Ideal.span {c} → R
hf₂ : ∀ (x : R ⧸ Ideal.span {c}), q₂ (f₂ x) = x
S₁ : Finset (BasicConstructibleSetData R) := Finset.image (fun x ↦ { f := c * f₁ x.f, n := x.n, g := g₁ x }) T₁
S₂ : Finset (BasicConstructibleSetData R) :=
  Finset.image (fun x ↦ { f := f₂ x.f, n := x.n + 1, g := Fin.cons c (g₂ x) }) T₂
⊢ comap Polynomial.C '' (zeroLocus (Set.range e.val) \ zeroLocus {f}) = (S₁ ∪ S₂).toSet

Tactic:
calc
      comap Polynomial.C '' (zeroLocus (.range e) \ zeroLocus {f})
        = comap q₁ '' (comap Polynomial.C ''
            (comap (mapRingHom q₁.toRingHom) ⁻¹' (zeroLocus (.range e) \ zeroLocus {f}))) ∪
          comap q₂ '' (comap Polynomial.C ''
            (comap (mapRingHom q₂.toRingHom) ⁻¹' (zeroLocus (.range e) \ zeroLocus {f}))) :=
        Set.image_of_range_union_range_eq_univ (by ext; simp) (by ext; simp)
          (by rw [Ideal.Quotient.mkₐ_toRingHom,
            ← range_comap_algebraMap_localization_compl_eq_range_comap_quotientMk,
            RingHom.algebraMap_toAlgebra]; exact Set.union_compl_self _) _
      _ = (⋃ C ∈ S₁, C.toSet) ∪ ⋃ C ∈ S₂, C.toSet := ?_
      _ = ⋃ C ∈ S₁ ∪ S₂, C.toSet := by
        simpa using (Set.biUnion_union (SetLike.coe S₁) S₂ _).symm
    congr 1
    · convert! congr(comap q₁.toRingHom '' $hT₁)
      · dsimp only [e₁]
        rw [Set.preimage_sdiff, preimage_comap_zeroLocus, preimage_comap_zeroLocus,
          Set.image_singleton, Pi.smul_def, ← Set.smul_set_range, Set.range_comp]
        congr 1
        refine (PrimeSpectrum.zeroLocus_smul_of_isUnit (.map _ ?_) _).symm
        exact isUnit_iff_exists_inv'.mpr ⟨_, IsLocalization.Away.mul_invSelf c⟩
      · rw [ConstructibleSetData.toSet, Set.image_iUnion₂]
        simp_rw [← Finset.mem_coe, S₁, Finset.coe_image, Set.biUnion_image]
        congr! with x hxT₁
        apply Set.injOn_preimage subset_rfl (f := comap q₁.toRingHom)
        · dsimp only [q₁, AlgHom.toRingHom_eq_coe]
          rw [IsScalarTower.coe_toAlgHom,
            localization_away_comap_range (S := Localization.Away c) (r := c),
            BasicConstructibleSetData.toSet, sdiff_eq, ← basicOpen_eq_zeroLocus_compl,
            basicOpen_mul]
          exact Set.inter_subset_right.trans Set.inter_subset_left
        · exact Set.image_subset_range ..
        · rw [BasicConstructibleSetData.toSet, BasicConstructibleSetData.toSet, Set.preimage_sdiff,
            preimage_comap_zeroLocus, preimage_comap_zeroLocus, Set.preimage_image_eq]
          swap; · exact localization_comap_injective _ (.powers c)
          simp only [AlgHom.toLinearMap_apply] at hq₁g₁
          simp only [← Set.range_comp, comp_def, AlgHom.toRingHom_eq_coe, RingHom.coe_coe,
            hq₁g₁ _ hxT₁, Set.image_singleton, map_mul, ← hf₁, mul_comm x.1, ← mul_assoc,
            ← pow_succ']
          simp only [← smul_eq_mul, ← Set.smul_set_range, ← Set.smul_set_singleton,
            zeroLocus_smul_of_isUnit ((isUnit_of_invertible (q₁ c)).pow _)]
    · convert! congr(comap q₂.toRingHom '' $hT₂)
      · rw [Set.preimage_sdiff, preimage_comap_zeroLocus, preimage_comap_zeroLocus,
          Set.image_singleton, Set.range_comp, AlgHom.toRingHom_eq_coe]
      · rw [ConstructibleSetData.toSet, Set.image_iUnion₂]
        simp_rw [← Finset.mem_coe, S₂, Finset.coe_image, Set.biUnion_image]
        congr! 3 with x hxT₂
        apply Set.injOn_preimage subset_rfl (f := comap q₂.toRingHom)
        · rw [range_comap_of_surjective _ _ q₂_surjective]
          simp only [AlgHom.toRingHom_eq_coe, Ideal.Quotient.mkₐ_ker, zeroLocus_span, q₂]
          exact Set.sdiff_subset.trans (zeroLocus_anti_mono (by simp))
        · exact Set.image_subset_range _ _
        · simp only [AlgHom.toLinearMap_apply] at hq₂g₂
          have : q₂ c = 0 := by simp [q₂]
          simp only [BasicConstructibleSetData.toSet, Set.preimage_sdiff, preimage_comap_zeroLocus,
            preimage_comap_zeroLocus,
            Set.preimage_image_eq _ (comap_injective_of_surjective _ q₂_surjective)]
          simp only [Fin.range_cons, Set.image_singleton, Set.image_insert_eq,
            ← Set.range_comp, comp_def]
          simp only [AlgHom.toRingHom_eq_coe, AlgHom.coe_toRingHom, hq₂g₂ _ hxT₂, hf₂]
          rw [← Set.union_singleton, zeroLocus_union,
            this, zeroLocus_singleton_zero, Set.inter_univ]

Goal state after: