Publications
Journal and conference papers, and contributions to the mathlib4 library.
Published
2026
2025
2021
Formalization: merged into mathlib4
- feat(CategoryTheory/Abelian/Preradical): introduce and characterize radicalsMar 2026Following Stenström, a preradical ‘Φ‘ is called radical if it coincides with its self colon. We encode this as the existence of an isomorphism ‘Φ.colon Φ ≅ Φ‘. We then prove a basic characterization of radical preradicals in terms of the vanishing of ‘Φ.r‘ on ‘Φ.quotient‘.
- feat(CategoryTheory/Abelian/Preradical): add Stenström’s colon construction for preradicalsMar 2026Given preradicals ‘Φ‘ and ‘Ψ‘ on an abelian category ‘C‘, this file defines their colon ‘Φ : Ψ‘ in the sense of Stenström. Categorically, ‘Φ : Ψ‘ is constructed objectwise as a pullback of the canonical projection ‘Φ.π X : X ⟶ Φ.quotient.obj X‘ along the inclusion ‘Functor.whiskerLeft Φ.quotient Ψ.ι‘.
- feat(RingTheory/IdealFilter): add ideal filters and Gabriel filtersJan 2026Introduces ideal filters on rings and Gabriel filters in
mathlib4, including the uniformity conditions (T1–T3), Gabriel composition, and a characterization of Gabriel filters (T4). Preparatory infrastructure for relating Gabriel filters to Giraud subcategories; merged intomathlib4via PR #33021 - feat(RingTheory/IdealFilter): topologies associated to ideal filtersFeb 2026Introduces additive and ring topologies on rings arising from ideal filters in
mathlib4, including constructions of additive and ring filter bases, characterizations of uniform ideal filters via the existence of a ring filter basis, neighborhood descriptions of the induced topologies, and a proof that the resulting ring topology is linear; provides the topological counterpart to the algebraic theory of ideal filters; merged intomathlib4via PR #33852.
Formalization: open pull requests
- feat(CategoryTheory/Subobject): kernels of pullbacks of subobjectsSep 2026Adds
Subobject.le_pullback_of_comp_eq_zero,Subobject.ofLE_comp_pullbackπ_eq_zeroandSubobject.isLimitKernelForkPullbackπ: for a morphismf : X ⟶ Yand subobjectsxofXandyofY, ifx.arrow ≫ f = 0thenxis contained in the pullback ofyalongf, the induced map into that pullback composed withpullbackπ f yvanishes, and if moreoverx.arrowis a kernel offthen that map is a kernel ofpullbackπ f y. These require onlyHasZeroMorphismsandHasPullbacks. Open pull request #44223. - feat(CategoryTheory/Abelian): short exact sequences from pulling back a subobjectSep 2026Pulling a subobject
BofYback along an epimorphismf : X ⟶ Ywhose kernel isAyields an extension ofBbyA; this records that as a short exact sequence in an abelian category. AddsshortComplexPullbackπandshortExact_shortComplexPullbackπ, together with the special casef = cokernel.π A.arrow, which is one direction of the correspondence between subobjects ofXcontainingAand subobjects of the quotient. Builds onSubobject.isLimitKernelForkPullbackπfrom #44223. Open pull request #44229. - feat(CategoryTheory/ObjectProperty): closure properties of orthogonals and S. E. Dickson’s theoremSep 2026Studies how the closure properties of a property of objects
Pinteract with the orthogonal complementsP.leftOrthogonalandP.rightOrthogonaland with passage to the opposite category. In a well-powered abelian category with coproducts, ifPis closed under quotients, extensions and coproducts thenP.rightOrthogonal.leftOrthogonal = P, the hard direction of S. E. Dickson’s characterization of torsion classes. Open pull request #44226. - feat(CategoryTheory/Abelian/TorsionTheory): Introduce torsion theory for abelian categoriesMar 2026Introduces torsion theories on an abelian category: a pair of object properties that are each other’s left and right orthogonals. Adds
Abelian.TorsionTheory, the typeclassesIsTorsionClassandIsTorsionFreeClass, the torsion theories generated and cogenerated by a property, transport alongopandunop, and Dickson’s theoremisTorsionClass_iff: in a well-powered abelian category with coproducts, a class is a torsion class if and only if it is closed under quotients, extensions and coproducts. Open pull request #36744.