Alphabeta Math

Category O Finiteness Duality and Blocks

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1 · Prerequisites
2 · Logical flowchart

3 · Items

Definition

The classical BGG category O

Lemma

Noetherianity of the enveloping algebra

Lemma

Finite Borel-stable generators and weight flags

Proposition

The support description of category O with finite generation

Proposition

Verma and finite-dimensional weight modules belong to O

Theorem

Category O is abelian and extension closed among weight modules

Lemma

A nonzero O-object has a highest-weight vector

Theorem

The simple objects of O

Lemma

Finite filtrations by highest-weight quotients

Lemma

The center has finite-dimensional image on each O-object

Definition

Generalized central-character subcategories

Lemma

Generalized central-character summands

Theorem

Generalized central-character decomposition of O

Lemma

Finite weight-space detection of subquotients

Theorem

Every object of O has finite length

Proposition

Verma composition multiplicities are finite

Theorem

The strong linkage principle for Verma modules

Lemma

A Verma embedding implies strong linkage

Theorem

The BGG criterion for homomorphisms between Verma modules

Proposition

Finite-dimensional Hom spaces in O

Definition

Restricted Chevalley dual

Lemma

Restricted self-duality of simple highest-weight modules

Proposition

Restricted duality is exact and involutive on O

Definition

Standard and costandard objects

Proposition

The simple socle of a costandard object

Definition

The integral Weyl group of a weight

Lemma

Integral reflection linkage is an equivalence relation

Lemma

Simple extensions cannot cross linkage classes

Lemma

Splitting finite-length modules across separated simple classes

Theorem

Central-character summands refine into linkage blocks

Corollary

Duality preserves linkage blocks and block orthogonality

Lemma

Verma self-extensions in O split

Proposition

Finite-dimensional tensoring preserves O

Definition

The Grothendieck group and character of O

Proposition

Simple and standard bases of K0(O)

Sources