Properties
- Whenever X ×Z Y exists, then so does Y ×Z X and there is an isomorphism X ×Z Y Y ×Z X.
- Monomorphisms are stable under pullback: if the arrow f above is monic, then so is the arrow p2. For example, in the category of sets, if X is a subset of Z, then, for any g : Y → Z, the pullback X ×Z Y is the inverse image of X under g.
- Isomorphisms are also stable, and hence, for example, X ×X Y Y for any map Y → X.
- Any category with pullbacks and products has equalizers.
Read more about this topic: Pullback (category Theory)
Famous quotes containing the word properties:
“A drop of water has the properties of the sea, but cannot exhibit a storm. There is beauty of a concert, as well as of a flute; strength of a host, as well as of a hero.”
—Ralph Waldo Emerson (1803–1882)
“The reason why men enter into society, is the preservation of their property; and the end why they choose and authorize a legislative, is, that there may be laws made, and rules set, as guards and fences to the properties of all the members of the society: to limit the power, and moderate the dominion, of every part and member of the society.”
—John Locke (1632–1704)