Principal Koszul positivity after restriction of scalars #
Support and torsion are computed over the coefficient algebra C; the
resulting length inequality is measured over the base ring R. No finite
generation of E over R is needed: only the first R-kernel has finite
length.
theorem
AlgebraicAnalysis.PrincipalKoszulSupportOverBase.length_cokernel_gt_kernel_of_support_over_base
{R : Type u}
{C : Type v}
{E : Type w}
[CommRing R]
[CommRing C]
[Algebra R C]
[AddCommGroup E]
[Module C E]
[Module R E]
[IsScalarTower R C E]
[IsNoetherianRing C]
[Module.Finite C E]
(x : C)
(p q : PrimeSpectrum C)
(hp : p ∈ Module.support C E)
(hpq : p ≤ q)
(hxp : x ∉ p.asIdeal)
(hq : q ∈ Module.support C (QuotSMulTop x E))
(hfinite : IsFiniteLength R ↥(↑R ((LinearMap.lsmul C E) x)).ker)
:
Module.length R (E ⧸ (↑R ((LinearMap.lsmul C E) x)).range) > Module.length R ↥(↑R ((LinearMap.lsmul C E) x)).ker