Fundamental Theorem of Topos Theory

In mathematics, the fundamental theorem of topos theory states that the slice of an elementary topos over any one of its objects is itself a topos. Moreover, if there is a morphism between two objects of the topos, there is a corresponding functor between their slice topoi that preserves exponentials and the subobject classifier. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/