category of empty-or-finite pairs of sets

Notation (Set×Set)∅,fin(\Set \times \Set)_{\varnothing,\fin} Objects pairs (A,B)(A,B) of sets AA and BB such that AA is empty or BB is finite Morphisms pairs of functions Related Set\Set, Set×Set\Set \times \Set, FinSet\FinSet

This is a rather random full subcategory of Set×Set\Set \times \Set. We have included it solely as an example of a category with a subobject classifier that does not have binary coproducts.

Satisfied Properties

Assigned properties

Deduced properties

Unsatisfied Properties

Assigned properties

Deduced properties*

*This also uses the deduced satisfied properties.

Unknown properties

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Special objects

  • terminal object: (1,1)(1,1)
  • initial object: (0,0)(0,0)
  • products: [finite case] component-wise direct product

Special morphisms

  • isomorphisms: pairs of bijective maps
  • monomorphisms: pairs of injective maps
  • epimorphisms: pairs of surjective maps
  • regular monomorphisms: same as monomorphisms
  • regular epimorphisms: same as epimorphisms