diff --git a/CommAlg/sayantan.lean b/CommAlg/sayantan.lean index 6140db5..7656924 100644 --- a/CommAlg/sayantan.lean +++ b/CommAlg/sayantan.lean @@ -9,11 +9,6 @@ import Mathlib.Order.ConditionallyCompleteLattice.Basic namespace Ideal -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 @@ -52,30 +47,36 @@ lemma dim_field_eq_zero {K : Type _} [Field K] : krullDim K = 0 := by unfold krullDim simp [field_prime_height_zero] +noncomputable +instance : CompleteLattice (WithBot ℕ∞) := + inferInstanceAs <| CompleteLattice (WithBot (WithTop ℕ)) + 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, ⟨h1, primeP⟩⟩ := x - have PgtBot : P > ⊥ := Ne.bot_lt h1 - have pos_height : ↑(Set.chainHeight {J | J < P}) > 0 := by - have : ⊥ ∈ {J | J < P} := PgtBot - have : {J | J < P}.Nonempty := Set.nonempty_of_mem this - -- have : {J | J < P} ≠ ∅ := Set.Nonempty.ne_empty this + let P' : PrimeSpectrum D := PrimeSpectrum.mk P primeP + have h2 : P' ≠ ⊥ := by + by_contra a + have : P = ⊥ := by rwa [PrimeSpectrum.ext_iff] at a + contradiction + have PgtBot : P' > ⊥ := Ne.bot_lt h2 + have pos_height : ¬ ↑(Set.chainHeight {J | J < P'}) ≤ 0 := by + have : ⊥ ∈ {J | J < P'} := PgtBot + have : {J | J < P'}.Nonempty := Set.nonempty_of_mem this rw [←Set.one_le_chainHeight_iff] at this - exact Iff.mp ENat.one_le_iff_pos this - have zero_height : ↑(Set.chainHeight {J | J < P}) = 0 := by - -- Probably need to use Sup_le or something here - sorry - have : ↑(Set.chainHeight {J | J < P}) ≠ 0 := Iff.mp pos_iff_ne_zero pos_height + exact not_le_of_gt (Iff.mp ENat.one_le_iff_pos this) + have zero_height : (Set.chainHeight {J | J < P'}) ≤ 0 := by + have : (⨆ (I : PrimeSpectrum D), (Set.chainHeight {J | J < I} : WithBot ℕ∞)) ≤ 0 := h.le + rw [iSup_le_iff] at this + exact Iff.mp WithBot.coe_le_zero (this P') contradiction 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 + let h : Field D := IsField.toField fieldD + exact dim_field_eq_zero \ No newline at end of file