Pushout (category theory)

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In category theory, a branch of mathematics, a pushout (also called a fibered coproduct or fibered sum or cocartesian square or amalgamated sum) is the colimit of a diagram consisting of two morphisms f : Z → X and g : Z → Y with a common domain. The pushout consists of an object P along with two morphisms X → P and Y → P that complete a commutative square with the two given morphisms f and g. In fact, the defining universal property of the pushout (given below) essentially says that the pushout is the "most general" way to complete this commutative square. Common notations for the pushout are P = X ⊔ Z Y {\displaystyle P=X\sqcup _{Z}Y} and P = X + Z Y {\displaystyle P=X+_{Z}Y} . The pushout is the categorical dual of the pullback.

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