# Yoneda lemma

Definition from Wiktionary, the free dictionary

## Contents

## English[edit]

### Etymology[edit]

Lemma named after the Japanese mathematician Nobuo Yoneda.

### Noun[edit]

- (category theory) Given a category
*C*with an object*A*, let*H*^{A}be a representable functor from*C*to the category of**Sets**, and let*F*be any functor from*C*to**Sets**, then there is a "natural" isomorphism between the set*F*(*A*) and Nat(*H*^{A},*F*), the set of natural transformations from*H*^{A}to*F*.