nLab categorical shape theory


In the original form of abstract shape theory, the restrictions that (i) it should refer to a subcategory of ‘nice’ or ‘good’ objects, and (ii) that subcategory should be pro-reflective (shape theorist's 'dense') were unnecessarily restrictive, eliminating interesting situations where similar constructions could be useful, and tended to obscure the nature of certain of the results, which were more much general than was initially apparent.

This was explored by Deleanu and Hilton in the early 1970s.


Let K:DCK : D\to C be a functor. The shape category of KK is the category with objects the same objects as those of CC but with morphisms from cc to c c^\prime being the functors between the corresponding comma categories (c )/K)(c^\prime)/K) and (c/K)(c/K) (note reversal of order) that are compatible with the codomain functors to DD.

(More to come later!)

Last revised on March 26, 2010 at 23:48:40. See the history of this page for a list of all contributions to it.