Cocomplete toposes whose exact completions are toposes

Let epsilon be a cocomplete topos. We show that if the exact completion of E is a topos then every indecomposable object in epsilon is an atom. As a corollary we characterize the locally connected Grothendieck toposes whose exact completions are toposes. This result strengthens both the Lawvere-Schanuel characterization of Boolean presheaf toposes and Hofstra's characterization of the locally connected Grothendieck toposes whose exact completion is a Grothendieck topos. We also show that for any topological space X, the exact completion of Sh(X) is a topos if and only if X is discrete. The corollary in this case characterizes the Grothendieck toposes with enough points whose exact completions are toposes. (C) 2006 Elsevier B.V. All rights reserved.