diff --git a/CommAlg/sayantan(poly_over_field).lean b/CommAlg/sayantan(poly_over_field).lean new file mode 100644 index 0000000..5379c52 --- /dev/null +++ b/CommAlg/sayantan(poly_over_field).lean @@ -0,0 +1,45 @@ +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 + +lemma polynomial_over_field_dim_one {K : Type} [Nontrivial K] [Field K] : krullDim (Polynomial K) = 1 := by + -- unfold krullDim + rw [le_antisymm_iff] + constructor + · 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 + 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] + suffices : P.asIdeal ≠ ⊥ + · by_contra x + rw [PrimeSpectrum.ext_iff] at x + contradiction + by_contra x + simp only [span_singleton_eq_bot] at x + have := @Polynomial.X_ne_zero K _ _ + contradiction + have : {J | J < P}.Nonempty := Set.nonempty_of_mem this + rwa [←Set.one_le_chainHeight_iff, ←WithBot.one_le_coe] at this