diff --git a/CommAlg/krull.lean b/CommAlg/krull.lean index bf3e998..b346d4d 100644 --- a/CommAlg/krull.lean +++ b/CommAlg/krull.lean @@ -60,7 +60,8 @@ lemma height_le_krullDim (I : PrimeSpectrum R) : height I ≤ krullDim R := le_iSup (λ I : PrimeSpectrum R => (height I : WithBot ℕ∞)) I /-- In a domain, the height of a prime ideal is Bot (0 in this case) iff it's the Bot ideal. -/ -lemma height_bot_iff_bot {D: Type} [CommRing D] [IsDomain D] (P : PrimeSpectrum D) : height P = ⊥ ↔ P = ⊥ := by +@[simp] +lemma height_bot_iff_bot {D: Type} [CommRing D] [IsDomain D] {P : PrimeSpectrum D} : height P = ⊥ ↔ P = ⊥ := by constructor · intro h unfold height at h @@ -263,7 +264,7 @@ lemma dim_eq_zero_iff [Nontrivial R] : krullDim R = 0 ↔ ∀ I : PrimeSpectrum /-- In a field, the unique prime ideal is the zero ideal. -/ @[simp] -lemma field_prime_bot {K: Type _} [Field K] (P : Ideal K) : IsPrime P ↔ P = ⊥ := by +lemma field_prime_bot {K: Type _} [Field K] {P : Ideal K} : IsPrime P ↔ P = ⊥ := by constructor · intro primeP obtain T := eq_bot_or_top P @@ -274,9 +275,13 @@ lemma field_prime_bot {K: Type _} [Field K] (P : Ideal K) : IsPrime P ↔ P = exact bot_prime /-- In a field, all primes have height 0. -/ -lemma field_prime_height_bot {K: Type _} [Field K] (P : PrimeSpectrum K) : height P = ⊥ := by - -- This should be doable by using field_prime_height_bot - -- and height_bot_iff_bot +lemma field_prime_height_bot {K: Type _} [Nontrivial K] [Field K] {P : PrimeSpectrum K} : height P = ⊥ := by + -- This should be doable by + -- have : IsPrime P.asIdeal := P.IsPrime + -- rw [field_prime_bot] at this + -- have : P = ⊥ := PrimeSpectrum.ext P ⊥ this + -- rw [height_bot_iff_bot] + -- Need to check what's happening rw [bot_eq_zero] unfold height simp only [Set.chainHeight_eq_zero_iff] diff --git a/CommAlg/sayantan(poly_over_field).lean b/CommAlg/sayantan(poly_over_field).lean index 987fe93..367e30f 100644 --- a/CommAlg/sayantan(poly_over_field).lean +++ b/CommAlg/sayantan(poly_over_field).lean @@ -1,39 +1,71 @@ import CommAlg.krull import Mathlib.RingTheory.Ideal.Operations -import Mathlib.RingTheory.FiniteType import Mathlib.Order.Height import Mathlib.RingTheory.PrincipalIdealDomain import Mathlib.RingTheory.DedekindDomain.Basic -import Mathlib.RingTheory.Ideal.Quotient -import Mathlib.RingTheory.Ideal.MinimalPrime -import Mathlib.RingTheory.Localization.AtPrime import Mathlib.AlgebraicGeometry.PrimeSpectrum.Basic -import Mathlib.Order.ConditionallyCompleteLattice.Basic namespace Ideal +/-- The ring of polynomials over a field has dimension one. -/ lemma polynomial_over_field_dim_one {K : Type} [Nontrivial K] [Field K] : krullDim (Polynomial K) = 1 := by - -- unfold krullDim rw [le_antisymm_iff] + let X := @Polynomial.X K _ constructor - · - sorry + · unfold krullDim + apply @iSup_le (WithBot ℕ∞) _ _ _ _ + intro I + have PIR : IsPrincipalIdealRing (Polynomial K) := by infer_instance + by_cases I = ⊥ + · rw [← height_bot_iff_bot] at h + simp only [WithBot.coe_le_one, ge_iff_le] + rw [h] + exact bot_le + · push_neg at h + have : I.asIdeal ≠ ⊥ := by + by_contra a + have : I = ⊥ := PrimeSpectrum.ext I ⊥ a + contradiction + have maxI := IsPrime.to_maximal_ideal this + have singleton : ∀P, P ∈ {J | J < I} ↔ P = ⊥ := by + intro P + constructor + · intro H + simp only [Set.mem_setOf_eq] at H + by_contra x + push_neg at x + have : P.asIdeal ≠ ⊥ := by + by_contra a + have : P = ⊥ := PrimeSpectrum.ext P ⊥ a + contradiction + have maxP := IsPrime.to_maximal_ideal this + have IneTop := IsMaximal.ne_top maxI + have : P ≤ I := le_of_lt H + rw [←PrimeSpectrum.asIdeal_le_asIdeal] at this + have : P.asIdeal = I.asIdeal := Ideal.IsMaximal.eq_of_le maxP IneTop this + have : P = I := PrimeSpectrum.ext P I this + replace H : P ≠ I := ne_of_lt H + contradiction + · intro pBot + simp only [Set.mem_setOf_eq, pBot] + exact lt_of_le_of_ne bot_le h.symm + replace singleton : {J | J < I} = {⊥} := Set.ext singleton + unfold height + sorry · suffices : ∃I : PrimeSpectrum (Polynomial K), 1 ≤ (height I : WithBot ℕ∞) · obtain ⟨I, h⟩ := this have : (height I : WithBot ℕ∞) ≤ ⨆ (I : PrimeSpectrum (Polynomial K)), ↑(height I) := by apply @le_iSup (WithBot ℕ∞) _ _ _ I exact le_trans h this have primeX : Prime Polynomial.X := @Polynomial.prime_X K _ _ - let X := @Polynomial.X K _ have : IsPrime (span {X}) := by - refine Iff.mpr (span_singleton_prime ?hp) primeX + refine (span_singleton_prime ?hp).mpr primeX exact Polynomial.X_ne_zero let P := PrimeSpectrum.mk (span {X}) this unfold height use P have : ⊥ ∈ {J | J < P} := by - simp only [Set.mem_setOf_eq] - rw [bot_lt_iff_ne_bot] + simp only [Set.mem_setOf_eq, bot_lt_iff_ne_bot] suffices : P.asIdeal ≠ ⊥ · by_contra x rw [PrimeSpectrum.ext_iff] at x