# 拉回 Pullbacks

$P=X\times _{Z}Y.$

In category theory, a branch of mathematics, a pullback (also called a fiber product, fibre product, fibered product or Cartesian square) is the limit of a diagram consisting of two morphisms $f:X \to Z$ and $g:Y \to Z$ with a common codomain. The pullback is often written

$P=X\times _{Z}Y.$

## 性质

• 如果 $X ×_{Z}Y$