nLab things to be categorified

This page contains ideas of concepts and constructions which might be profitably categorified.

Galois theory for algebraic extensions

Jeff Morton and John Baez apparently

… figured out how to categorify the algebraic integers in any algebraic extension of the rationals, getting an “algebraic extension” of the category of finite sets. We figured out the beginnings of a theory that associates a “Galois 2-group” to any such algebraic extension.


The Yoneda embedding of a category 𝒞\mathcal{C} to F(𝒞)=[𝒞 op,Set]F(\mathcal{C}) = [\mathcal{C}^{op}, Set] is a 2-coalgebra for the 2-endofunctor FF.

Like with the powerset functor there surely can’t be a terminal 2-coalgebra for FF. What about G(𝒞)=1+A×𝒞G(\mathcal{C}) = 1 + A \times \mathcal{C}, where AA is a fixed category? The terminal 2-coalgebra would have as objects finite or infinite lists of objects of AA with lists of arrows of AA as morphisms.

Structure Types

A sketch of 2-structure types.

Riemann-Hilbert problem

For any representation of the fundamental group of a punctured Riemann surface, we can find a linear differential equation with holomorphic coefficients, such that the monodromies of the solutions realize this representation: discussion.

Last revised on July 4, 2009 at 11:19:14. See the history of this page for a list of all contributions to it.