Consider the following situation: R |- F |- L with F o R = id and F o L = id. I have derived a number of results about this situation, but probably this is already known in the literature? Under the name `Lawvere cylinders'? Till Mossakowski ----------------------------------------------------------------------------- Till Mossakowski Phone +49-421-218-4683, monday: +49-4252-1859 Dept. of Computer Science Fax +49-421-218-3054 University of Bremen till@informatik.uni-bremen.de P.O.Box 330440, D-28334 Bremen http://www.informatik.uni-bremen.de/~till -----------------------------------------------------------------------------