Hello, considering the category of categories, either with functors or with natural transformations as morphisms, or categories of functors with natural transformations as morphisms, it seems very likely to me that the basic questions like: -- what are the mono's, epi's, extreme mono's, extreme epi's etc. ? -- constant morphisms, initial and terminal objects etc. ? -- existence of limits and colimits ? have all been answered for these categories. But in the books known to me only very few facts are given. I started answering these questions myself, but some (like the characterisation of monomorphic functors or monomorphic natural transformations) seem not completely trivial to me. So my question: Could somebody tell me about sources regarding these basic considerations?! (I'm an outsider to category theory, and perhaps there are sources known to everybody in the list, but not to me; I would be glad for any help. Especially I would like to see any kind of an encyclopaedic source for category theory.) Thanks for your help in any case! Oliver -- Dr. Oliver Kullmann Computer Science Department University of Wales Swansea Faraday Building, Singleton Park Swansea SA2 8PP, UK http://cs-svr1.swan.ac.uk/~csoliver/ 18-Jan-2005 13:32:32 -0400,1108;000000000000-00000000