Definition:Subcategory

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Definition

Definition 1

Let $\mathbf C$ be a metacategory.


A subcategory of $\mathbf C$ is a metacategory with:

Objects:    Any collection of objects from $\mathbf C$      
Morphisms:    Any collection of morphisms from $\mathbf C$      
Composition:    Inherited from $\mathbf C$      
Identity morphisms:    Inherited from $\mathbf C$      

Colloquially, a subcategory of $\mathbf C$ is a "part of $\mathbf C$ that is a category in its own right".


Definition 2

Let $\mathbf C$ be a metacategory.


A subcategory of $\mathbf C$ is a monic functor $F: \mathbf D \to \mathbf C$ to $\mathbf C$


Also see


Sources