On the local cartesian closure of exact completions

This paper presents a necessary and sufficient condition on a category C with weak finite limits for its exact completion Cex to be (locally) cartesian closed. A paper by Carboni and Rosolini already claimed such a characterisation using a different property on C, but we shall show that weak finite limits are not enough for their proof to go through. We shall also indicate how to strengthen the hypothesis for that proof to work. It will become clear that, in the case of ex/lex completions, their characterisation is still valid and it coincides with the one presented here.