Extensive category

In mathematics, an extensive category is a category C with finite coproducts that are disjoint and well-behaved with respect to pullbacks. Equivalently, C is extensive if the coproduct functor from the product of the slice categories C/X × C/Y to the slice category C/(X + Y) is an equivalence of categories for all objects X and Y of C.

Examples

The categories Set and Top of sets and topological spaces, respectively, are extensive categories. More generally, the category of presheaves on any small category is extensive.

The category CRing^op of affine schemes is extensive.

External links

• Extensive category at the nLab