§6. Rel(9tf)-categories, sheaves and topologies

As was pointed out in Prop. 3.5.2., the opposite c o n ta in m e n t to f~^(OA) c 0 ( f _^(A)) a lways holds.

Following th e insight of Joya l ([JT]), we can now, as did Ghilardi and Meloni, define the notion of an etale Q-category.