Recall that the petit étale topos of a scheme *X* is the topos of sheaves on the category of schemes étale over *X* (with respect to the étale topology). Since étale morphisms are open, any closed sieve on *X* must contain the union of the (open) images of all its members. Thus, the closed sieves on *X* are classified by the open subspaces of *X*, so the localic reflection of the petit étale topos of *X* is the petit Zariski topos of *X*.

Note also that the same argument works for the petit fppf topos of *X* – the point being that flat morphisms locally of finite presentation are open.

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