Do (finite) colimits exist in categories of diagrams? Here are the definitions of the terms used above. A diagram of shape S in a category C is a functor D: S -> C. A covariant diagram morphism from D1: S1 -> C to D2: S2 -> C is a pair <sm, mu> consisting a shape morphism (functor) sm: S1 -> S2 and a natural transformation mu: D1 -> D2 o sm. A contravariant diagram morphism is similar except that the direction of the natural transformation is opposite. We thus get two categories of diagrams in C (of all shapes). Mac Lane calls these "super comma categories" (p.111). Now, the question reads: given that (finite) colimits exist in C, do (finite) colimits exist in the two categories of diagrams in C? I haven't been able to come up with a construction or a proof that colimits don't exist. I appreciate any help you can provide on this matter. Also, I would like to know if there are related results, e.g., with limits. - srinivas ======== Y. V. Srinivas E-mail: srinivas@kestrel.edu Kestrel Institute Phone: (415) 493-6871 3260 Hillview Avenue Fax: (415) 424-1807 Palo Alto, CA 94304