Principal Koszul positivity from minimal support #
The support primes used by the strict length argument are produced from the
finite C-module itself. In particular, no finiteness of E over the base
ring R is needed.
theorem
AlgebraicAnalysis.PrincipalKoszulMinimalSupportPositivity.length_cokernel_gt_kernel_of_minimal_support
{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)
(hmin : ∀ p ∈ (Module.annihilator C E).minimalPrimes, x ∉ p)
(hnonzero : Nontrivial (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
Minimal support primes of E produce the ordered support pair needed by
the principal Koszul positivity argument.