Changes

:The other example I'm thinking about adding is Hom(-,V) and Hom(V,-), both functors from Vect_k to Vect_k.  Given a fixed vector space V, Hom(-,V) is the functor that sends an object W in Vect_k to the set of linear maps from W to V, which is itself a vector space.  The first of these is contravariant and the second is covariant (or the other way, I always get it wrong), and it's easy to write down why.  It's a nice pair of examples in an easy-to-understand category. --[[User:MarkGall|MarkGall]] 17:00, 1 October 2009 (EDT)

:The other example I'm thinking about adding is Hom(-,V) and Hom(V,-), both functors from Vect_k to Vect_k.  Given a fixed vector space V, Hom(-,V) is the functor that sends an object W in Vect_k to the set of linear maps from W to V, which is itself a vector space.  The first of these is contravariant and the second is covariant (or the other way, I always get it wrong), and it's easy to write down why.  It's a nice pair of examples in an easy-to-understand category. --[[User:MarkGall|MarkGall]] 17:00, 1 October 2009 (EDT)