Published online by Cambridge University Press: 20 November 2018
Given a pair of maps
in a category, we would like to know whether they form part of a pullback diagram as follows:
I am indebted to Basil Rattray for mentioning the solution of this problem for the category of sets. Here we shall solve it for any regular category in the sense of Barr [1].
It will be useful to make the following definition.