A Universal Characterisation of Codescent Objects
arXiv:1709.01332
Abstract
In this work we define a 2-dimensional analogue of extranatural transformation and use these to characterise codescent objects. They will be seen as universal objects amongst extrapseudonatural transformations in a similar manner in which coends are universal objects amongst extranatural transformations. Some composition lemmas concerning these transformations are introduced and a Fubini theorem for codescent objects is proven using the universal characterisation description.
27 pages, adapted from material in the author's PhD Thesis, see http://etheses.whiterose.ac.uk/id/eprint/16767