Endofunctors of set and cardinalities A. Barkhudaryan, R. El Bashir, V. Trnková (2003) Cahiers de Topologie et Géométrie Différentielle Catégoriques
Every group is representable by all natural transformations of some set-functor. Barto, Libor, Zima, Petr (2005) Theory and Applications of Categories [electronic only]
Exactness of the set-valued colim Jiří Adámek, Jan Reiterman (1976) Commentationes Mathematicae Universitatis Carolinae