Definition:Underlying Set Functor

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Definition

Let $\mathbf {Set}$ be the category of sets.

Let $\mathbf C$ be a metacategory with:

A collection of sets as objects;
A collection of mappings as morphisms.


The underlying set functor $\size {\, \cdot \,}: \mathbf C \to \mathbf {Set}$ is defined in the following cases.



Category of Monoids

Let $\mathbf {Mon}$ be the category of monoids.

The underlying set functor $\size {\, \cdot \,}: \mathbf {Mon} \to \mathbf {Set}$ is the functor defined by:

Object functor:    \(\ds \size {\struct {M, \circ} } := M \)      
Morphism functor:    \(\ds \size f := f \)      


Sources