Australian Category Seminar

Preservation of finite connected limits

Robert Paré·26 Feburary 1986

Proposition 1. A category has finite connected limits iff it has pullbacks and equalizers.

Proposition 2. A functor between finitely complete categories preserves finite comnected limits if it preserves pullbacks.

Example. Categories A\mathcal{A} and B\mathcal{B} have finite connected limits and F ⁣:ABF \colon \mathcal{A} \to \mathcal{B} preserves pullbacks but doesn't preserve equalizers. (Let f ⁣:HGf \colon H \to G be a non one-one group homomorphism. Build a category G\mathcal{G} out of GG by considering it as a one object category and formally adjoining an initial object. Do the same for HH and define a functor in the obvious way. This last mentioned functor is an example of the above.)

Question: Why are the finite limits needed in proposition 2? Or rather, what is the AA and BB have limits of finite connected diagrams which admit a cocone, then FF preserves these iff FF preserves pullbacks.

Back