Merge pull request #77 from GTBarkley/grant

Grant

CommAlg/grant2.lean

@@ -0,0 +1,62 @@
+import Mathlib.Order.KrullDimension
+import Mathlib.Order.JordanHolder
+import Mathlib.AlgebraicGeometry.PrimeSpectrum.Basic
+import Mathlib.Order.Height
+import Mathlib.RingTheory.Noetherian
+import CommAlg.krull
+
+variable (R : Type _) [CommRing R] [IsNoetherianRing R]
+
+lemma height_le_of_gt_height_lt {n : ℕ∞} (q : PrimeSpectrum R)
+  (h : ∀(p : PrimeSpectrum R), p < q → Ideal.height p ≤ n - 1) : Ideal.height q ≤ n := by
+  sorry
+   
+
+theorem height_le_one_of_minimal_over_principle (p : PrimeSpectrum R) (x : R):
+  p ∈ minimals (· < ·) {p | x ∈ p.asIdeal} → Ideal.height p ≤ 1 := by
+  intro h
+  apply height_le_of_gt_height_lt _ p
+  intro q qlep
+  by_contra hcontr
+  push_neg at hcontr
+  simp only [le_refl, tsub_eq_zero_of_le] at hcontr 
+  
+  sorry
+
+#check (_ : Ideal R) ^ (_ : ℕ)
+#synth Pow (Ideal R) (ℕ)
+
+def symbolicIdeal(Q : Ideal R) {hin : Q.IsPrime} (I : Ideal R) : Ideal R where
+  carrier := {r : R | ∃ s : R, s ∉ Q ∧ s * r ∈ I}
+  zero_mem' := by
+    simp only [Set.mem_setOf_eq, mul_zero, Submodule.zero_mem, and_true]
+    use 1
+    rw [←Q.ne_top_iff_one]
+    exact hin.ne_top
+  add_mem' := by
+    rintro a b ⟨sa, hsa1, hsa2⟩ ⟨sb, hsb1, hsb2⟩
+    use sa * sb
+    constructor
+    . intro h
+      cases hin.mem_or_mem h <;> contradiction
+    ring_nf
+    apply I.add_mem --<;> simp only [I.mul_mem_left, hsa2, hsb2]
+    . rw [mul_comm sa, mul_assoc]
+      exact I.mul_mem_left sb hsa2 
+    . rw [mul_assoc]
+      exact I.mul_mem_left sa hsb2
+  smul_mem' := by
+    intro c x
+    dsimp
+    rintro ⟨s, hs1, hs2⟩
+    use s
+    constructor; exact hs1
+    rw [←mul_assoc, mul_comm s, mul_assoc]
+    exact Ideal.mul_mem_left _ _ hs2
+
+protected lemma LocalRing.height_le_one_of_minimal_over_principle
+  [LocalRing R] (q : PrimeSpectrum R) {x : R} 
+  (h : (closedPoint R).asIdeal ∈ (Ideal.span {x}).minimalPrimes) :
+  q = closedPoint R ∨ Ideal.height q = 0 := by
+  
+  sorry

CommAlg/krull.lean

@@ -33,6 +33,8 @@ noncomputable def height : ℕ∞ := Set.chainHeight {J : PrimeSpectrum R | J <
 
 noncomputable def krullDim (R : Type _) [CommRing R] : WithBot ℕ∞ := ⨆ (I : PrimeSpectrum R), height I
 
+noncomputable def codimension (J : Ideal R) : WithBot ℕ∞ := ⨅ I ∈ {I : PrimeSpectrum R | J ≤ I.asIdeal}, 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