diff --git a/CommAlg/grant.lean b/CommAlg/grant.lean index 7951c54..ce5041d 100644 --- a/CommAlg/grant.lean +++ b/CommAlg/grant.lean @@ -95,7 +95,7 @@ lemma krullDim_nonneg_of_nontrivial [Nontrivial R] : ∃ n : ℕ∞, Ideal.krull -- lemma krullDim_ge_iff' (R : Type _) [CommRing R] {n : WithBot ℕ∞} : -- Ideal.krullDim R ≥ n ↔ ∃ c : List (PrimeSpectrum R), c.Chain' (· < ·) ∧ c.length = n + 1 := sorry -lemma prime_elim_of_subsingleton (x : PrimeSpectrum R) [Subsingleton R] : False := +lemma primeSpectrum_empty_of_subsingleton (x : PrimeSpectrum R) [Subsingleton R] : False := x.1.ne_top_iff_one.1 x.2.1 <| Eq.substr (Subsingleton.elim 1 (0 : R)) x.1.zero_mem lemma primeSpectrum_empty_iff : IsEmpty (PrimeSpectrum R) ↔ Subsingleton R := by @@ -107,15 +107,16 @@ lemma primeSpectrum_empty_iff : IsEmpty (PrimeSpectrum R) ↔ Subsingleton R := by_contra hneg rw [not_isEmpty_iff] at hneg rcases hneg with ⟨a, ha⟩ - exact prime_elim_of_subsingleton R ⟨a, ha⟩ + exact primeSpectrum_empty_of_subsingleton R ⟨a, ha⟩ +/-- A ring has Krull dimension -∞ if and only if it is the zero ring -/ lemma dim_eq_bot_iff : krullDim R = ⊥ ↔ Subsingleton R := by unfold Ideal.krullDim rw [←primeSpectrum_empty_iff, iSup_eq_bot] constructor <;> intro h . rw [←not_nonempty_iff] rintro ⟨a, ha⟩ - specialize h ⟨a, ha⟩ + -- specialize h ⟨a, ha⟩ tauto . rw [h.forall_iff] trivial diff --git a/CommAlg/krull.lean b/CommAlg/krull.lean index 9b4c785..c021d74 100644 --- a/CommAlg/krull.lean +++ b/CommAlg/krull.lean @@ -62,7 +62,31 @@ lemma krullDim_eq_height [LocalRing R] : krullDim R = height (closedPoint R) := #check height_le_krullDim --some propositions that would be nice to be able to eventually -lemma dim_eq_bot_iff : krullDim R = ⊥ ↔ Subsingleton R := sorry +lemma primeSpectrum_empty_of_subsingleton (x : PrimeSpectrum R) [Subsingleton R] : False := + x.1.ne_top_iff_one.1 x.2.1 <| Eq.substr (Subsingleton.elim 1 (0 : R)) x.1.zero_mem + +lemma primeSpectrum_empty_iff : IsEmpty (PrimeSpectrum R) ↔ Subsingleton R := by + constructor + . contrapose + rw [not_isEmpty_iff, ←not_nontrivial_iff_subsingleton, not_not] + apply PrimeSpectrum.instNonemptyPrimeSpectrum + . intro h + by_contra hneg + rw [not_isEmpty_iff] at hneg + rcases hneg with ⟨a, ha⟩ + exact primeSpectrum_empty_of_subsingleton ⟨a, ha⟩ + +/-- A ring has Krull dimension -∞ if and only if it is the zero ring -/ +lemma dim_eq_bot_iff : krullDim R = ⊥ ↔ Subsingleton R := by + unfold Ideal.krullDim + rw [←primeSpectrum_empty_iff, iSup_eq_bot] + constructor <;> intro h + . rw [←not_nonempty_iff] + rintro ⟨a, ha⟩ + specialize h ⟨a, ha⟩ + tauto + . rw [h.forall_iff] + trivial lemma dim_eq_zero_iff_field [IsDomain R] : krullDim R = 0 ↔ IsField R := by sorry