Kernel support over a base ring #
A finite module over a commutative Noetherian coefficient algebra is Hopfian over that algebra. This gives the kernel--cokernel support inclusion after restriction of scalars, without assuming finite generation over the base.
theorem
AlgebraicAnalysis.endomorphism_kernel_support_subset_cokernel_support_over_base
{R : Type u_1}
{C : Type u_2}
{E : Type u_3}
[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]
(f : Module.End C E)
:
Module.support R ↥(↑R f).ker ⊆ Module.support R (E ⧸ (↑R f).range)