Quotient–submodule equidistribution conjecture

For every finite-dimensional representation-finite algebra AA and every integer i0i\ge 0, the number of quotient-closed full additive subcategories CmodA\mathcal{C}\subseteq \operatorname{mod}A satisfying ind(C)=i|\operatorname{ind}(\mathcal{C})|=i equals the number of submodule-closed full additive subcategories DmodA\mathcal{D}\subseteq \operatorname{mod}A satisfying ind(D)=i|\operatorname{ind}(\mathcal{D})|=i. Here quotient-closed means closed under factor modules, submodule-closed means closed under submodules, and ind(C)|\operatorname{ind}(\mathcal{C})| denotes the number of isomorphism classes of indecomposable modules in C\mathcal{C}, with analogous notation for D\mathcal{D}.

Progress summary

Partially solved

Several important special cases are now proved, but the full conjecture remains open.

The conjecture predicts an equidistribution phenomenon connecting categorical enumeration with Bruhat intervals and convex-geometric structure. Its general representation-finite case is not settled.

August 2026 special-case results

The conjecture is proved for extreme sizes, Nakayama algebras, radical-square-zero algebras, and representation-directed algebras. The general representation-finite case remains open.

Current status (as of August 2026): Several substantial algebra classes and extreme-size cases are settled, while the general representation-finite case remains open.

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