CatDat

category of sets with finite-to-one maps

  • notation: Setf\Set_\f
  • objects: sets
  • morphisms: maps f:XYf : X \to Y with the property that for every yYy \in Y the fiber f({y})f^*(\{y\}) is a finite set
  • Related categories: FinSet\FinSetSet\Set

In this variant of Set\Set we only consider maps with finite fibers, which are commonly called finite-to-one. Equivalently, every preimage of a finite set is again finite, and this description makes it obvious that composition is well-defined.

Satisfied Properties

Assigned properties

Deduced properties

Unsatisfied Properties

Assigned properties

Deduced properties*

*This also uses the deduced satisfied properties.

Unknown properties

Special objects

  • initial object: empty set
  • coproducts: [finite case] disjoint union

Special morphisms

  • isomorphisms: bijective maps
  • monomorphisms: injective maps
  • epimorphisms: surjective maps with finite fibers
  • regular monomorphisms: same as monomorphisms
  • regular epimorphisms: same as epimorphisms