Take the 2-minute tour ×
Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

Can anyone explain to me Yoneda Lemma proof in great details? i.e. they usually say " ... it is easy to see that these morphisms are inverse to each other.." without explanation.

share|improve this question
Perhaps it would be better if you explained what parts of the Yoneda lemma's proof you understand, and we can help with the bits that are unclear? If the only problem is understanding why the Yoneda embedding is fully faithful, there are two steps. For faithful, if a morphism $f$ is sent to a natural transformation $\eta$ in the functor category, we can recover $f$ by applying $\eta$ to the identity map. Therefore, no two different maps can be sent to the same transformation. For full, the definition of natural transformation implies that the image of the identity map determines everything. –  Aaron Dec 25 '11 at 9:24
thanks for the comment. –  user17090 Dec 25 '11 at 10:13
You would learn more if you try it yourself. –  Martin Brandenburg Jan 5 '12 at 13:37
Probably the most detailled proof can be found in Tom Leinster's new book "Basic Category theory". –  Martin Brandenburg Apr 23 at 13:55

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.