Limits, colimits, and adjoints: I go along with this: it is the result of general category theory that I have used most in studying colimits of forms of multiple groupoids, for homotopical applications. It really does come under `categories for the working mathematician'. I have also been attracted in the same vein by fibrations and cofibrations of categories: see a recent paper in TAC. I well remember a remark of Henry Whitehead in response to a visiting lecturer saying: `The proof is trivial.' JHCW: `It is the snobbishness of the young to suppose that a theorem is trivial because the proof is trivial.' (There was and is no answer to that!) (His example was Schroder-Bernstein.) The leads to the interesting question of what makes a theorem nontrivial? Good discussion topic for the young (at heart). Ronnie Brown [For admin and other information see: http://www.mta.ca/~cat-dist/ ]