diff --git a/CommAlg/sayantan.lean b/CommAlg/sayantan.lean index 553fa4f..b2fc79a 100644 --- a/CommAlg/sayantan.lean +++ b/CommAlg/sayantan.lean @@ -6,40 +6,24 @@ import Mathlib.RingTheory.Ideal.Quotient import Mathlib.RingTheory.Localization.AtPrime import Mathlib.AlgebraicGeometry.PrimeSpectrum.Basic import Mathlib.Order.ConditionallyCompleteLattice.Basic --- import Mathlib.Data.ENat.Lattice --- import Mathlib.Order.OrderIsoNat --- import Mathlib.Tactic.TFAE namespace Ideal --- def foo : List Nat := [1, 2, 3, 4, 5] - --- #check List.Chain' - --- example : List.Chain' (· < ·) foo := by --- repeat { constructor; norm_num } - - - example (x : Nat) : List.Chain' (· < ·) [x] := by constructor variable {R : Type _} [CommRing R] (I : PrimeSpectrum R) - noncomputable def height : ℕ∞ := Set.chainHeight {J : PrimeSpectrum R | J < I} - noncomputable def krullDim (R : Type) [CommRing R] : WithBot ℕ∞ := ⨆ (I : PrimeSpectrum R), height I lemma height_def : height I = Set.chainHeight {J : PrimeSpectrum R | J < I} := rfl lemma krullDim_def (R : Type) [CommRing R] : krullDim R = (⨆ (I : PrimeSpectrum R), height I : WithBot ℕ∞) := rfl lemma krullDim_def' (R : Type) [CommRing R] : krullDim R = iSup (λ I : PrimeSpectrum R => (height I : WithBot ℕ∞)) := rfl -variable {K : Type _} [Field K] - -lemma dim_field_eq_zero : krullDim K = 0 := by - have prime_bot (P : Ideal K) : IsPrime P ↔ P = ⊥ := by +@[simp] +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 @@ -48,9 +32,8 @@ lemma dim_field_eq_zero : krullDim K = 0 := by · intro botP rw [botP] exact bot_prime - unfold krullDim - have height_zero : ∀ P : PrimeSpectrum K, height P = 0 := by - intro P + +lemma field_prime_height_zero {K: Type _} [Field K] (P : PrimeSpectrum K) : height P = 0 := by unfold height simp by_contra spec @@ -59,9 +42,30 @@ lemma dim_field_eq_zero : krullDim K = 0 := by obtain ⟨J, JlP : J < P⟩ := spec have P0 : IsPrime P.asIdeal := P.IsPrime have J0 : IsPrime J.asIdeal := J.IsPrime - rw [prime_bot] at P0 J0 + rw [field_prime_bot] at P0 J0 have : J.asIdeal = P.asIdeal := Eq.trans J0 (Eq.symm P0) - have JeqP : J = P := PrimeSpectrum.ext J P this - have JneqP : J ≠ P := ne_of_lt JlP + have : J = P := PrimeSpectrum.ext J P this + have : J ≠ P := ne_of_lt JlP contradiction - simp [height_zero] + +lemma dim_field_eq_zero {K : Type _} [Field K] : krullDim K = 0 := by + unfold krullDim + simp [field_prime_height_zero] + +lemma isField.dim_zero {D: Type _} [CommRing D] [IsDomain D] (h: krullDim D = 0) : IsField D := by + unfold krullDim at h + simp [height] at h + by_contra x + rw [Ring.not_isField_iff_exists_prime] at x + obtain ⟨P, ⟨h, primeP⟩⟩ := x + have PgtBot : P > ⊥ := Ne.bot_lt h + sorry + +lemma dim_eq_zero_iff_field {D: Type _} [CommRing D] [IsDomain D] : krullDim D = 0 ↔ IsField D := by + constructor + · exact isField.dim_zero + · intro fieldD + have : Field D := IsField.toField fieldD + -- Not exactly sure why this is failing + -- apply @dim_field_eq_zero D _ + sorry