Let C be a category and F, G : C -> C be endo-functors. I denote the category of all F-algebras by Alg_C F and the canonical forgettable functor by U_F : Alg_C F -> C. I'm interested in concrete functors H : Alg_C F -> Alg_C G where `concrete' indicates the property U_F = U_G . H Does anybody know about such functors? Thanks for any help/references! Claus -------------------------------------------------------------------------------- Dipl.-Math. Claus Juergensen | Technische Universitaet Dresden e-mail: claus@orchid.inf.tu-dresden.de | Fakultaet Informatik phone: +49 (0)3 51 46 3 - 82 53 | Institut fuer Theoretische Informatik Lehrstuhl Grundlagen der Programmierung | D-01062 Dresden http://orchid.inf.tu-dresden.de/gdp/ | Germany --------------------------------------------------------------------------------