Annihilated nonunits make the idealization a total quotient ring
OpenMathoverflow507128.isFractionRing_self_of_kills_nonunitscommutative-algebrainvertible-modulespicard-groups
Let be a commutative ring and a -module. If every nonunit of annihilates a nonzero element of , then the trivial square-zero extension is a total ring of fractions of itself.
Preamble
import Mathlib.Algebra.TrivSqZeroExt.Basic import Mathlib.LinearAlgebra.TensorProduct.Prod import Mathlib.RingTheory.Localization.FractionRing import Mathlib.RingTheory.PicardGroup import Definitions.Def_RybinP18_CuspidalCubicInput import Definitions.Def_RybinP18_MO507128 /-! # MathOverflow 507128: the idealization step This file deliberately does not import or clone `formal-conjectures`. It copies the statement of the target theorem and proves the square-zero idealization argument using mathlib. The input for the idealization is constructed explicitly from the cuspidal cubic `Y² = X³`. Thus the final `#print axioms` contains no problem-specific axiom. -/
Formal statement
namespace Mathoverflow507128
universe u v
variable (D : Type u) [CommRing D]
variable (M : Type v) [AddCommGroup M] [Module D M]
local instance p2m_Theorems_Thm_Mathoverflow507128_isFractionRing_self_of_kills_nonunits_1 : Module Dᵐᵒᵖ M :=
Module.compHom M ((RingHom.id D).fromOpposite mul_comm)
local instance p2m_Theorems_Thm_Mathoverflow507128_isFractionRing_self_of_kills_nonunits_2 : IsCentralScalar D M := ⟨fun _ _ => rfl⟩
local notation "R" => TrivSqZeroExt D M
/-- If every nonunit of `D` kills a nonzero element of `M`, every regular
element of `D ⋉ M` is a unit. -/
theorem isFractionRing_self_of_kills_nonunits
(hkill : ∀ a : D, ¬ IsUnit a → ∃ m : M, m ≠ 0 ∧ a • m = 0) :
IsFractionRing R R := by
sorry
end Mathoverflow507128
namespace Mathoverflow507128
end Mathoverflow507128Source
CUHK-Shenzhen AI Math Problem 18, https://rybindmitry.github.io/problems/18.html. Lean formalization by Patricia Purtill and Kenta Kitamura, discussed at https://github.com/google-deepmind/formal-conjectures/pull/4644#issuecomment-5089566133; staged from Kenta Kitamura's Apache-2.0 repository https://github.com/KitaKen1/mo507128-lean at commit e9507429c01c4288089e4af1c92a03b7d1e17f74.